Doko.vn 341017 Nhan Dang Chu Viet Tay Tieng V

I HC THI NGUYN

TRNG I HC CNG NGH THNG TIN V TRUYN THNG

TRNH TH PHNG THO

NHN DNG CH VIT TAY TING VIT

S DNG MNG NRON

LUN VN THC S KHOA HC MY TNH

Thi Nguyn, Thng 06 nm 2012

S ha bi Trung tm Hc liu i hc Thi Nguyn http://www.lrc-tnu.edu.vn

i

LI CM N

Xin chn thnh cm n Thy gio, PGS.TS. L B Dng tn tnh ch

dy, hng dn ti trong sut thi gian nghin cu v thc hin lun vn.

Ti cng xin chn thnh cm n cc Thy gio Vin Cng ngh Thng tin

v cc Thy gio Trng Cng ngh thng tin v Truyn thng - H Thi

Nguyn ging dy, gip trong sut thi gian hc tp.

Xin cm n tt c cc anh ch hc vin Cao hc kha 9, cm n cc cn b

cng chc, ging vin Trng Cng ngh thng tin v Truyn thng - H Thi

Nguyn to iu kin tt cho ti trong sut trong hai nm hc qua.

Xin cm n cc bn b, ng nghip to diu kin cng nh ch bo

ti rt nhiu trong thi gian thc hin lun vn ny.

Cui cng, xin chn thnh cm n gia nh ng vin v to mi iu

kin thun li ti c c kt qu nh ngy hm nay.

Thi Nguyn, thng 06/2012

Ngi vit lun vn

Trnh Th Phng Tho


ii

LI CAM OAN

Ti xin cam oan ti lun vn Nhn dng ch vit tay Ting Vit s

dng mng Nron l cng trnh nghin cu ca bn thn ti. Cc s liu, kt

qu nghin cu nu trong lun vn ny l trung thc v khng sao chp y nguyn

t mt cng trnh no khc. Ti xin chu trch nhim v lun vn ca mnh.

Thi Nguyn, thng 06/2012

Ngi vit lun vn

Trnh Th Phng Tho


iii

MC LC

Trang

TRANG PH BA ..................................................................................................

LI CM N .......................................................................................................... i

LI CAM OAN ...................................................................................................ii

MC LC ............................................................................................................. iii

DANH MC CC T TING ANH VIT TT ................................................vii

DANH MC CC HNH ................................................................................... viii

PHN M U ..................................................................................................... 1

CHNG I ............................................................................................................. 3

TNG QUAN V MNG NRON NHN TO V MNG NRON

KOHONEN ............................................................................................................. 3

1.1. Gii thiu v mng nron nhn to .............................................................. 3

1.1.1 Lch s pht trin ..................................................................................... 3

1.1.2. M hnh mng n-ron nhn to .............................................................. 4

1.1.2.1. N-ron sinh hc ............................................................................... 4

1.1.2.2. N-ron nhn to ............................................................................... 6

1.1.2.3. Mng n-ron nhn to .................................................................... 12

1.1.2.3.1. Mng truyn thng ................................................................. 13

1.1.2.3.2. Mng hi quy (Recurrent Neutral Network) .......................... 15

1.1.2.4. Lut hc ......................................................................................... 16

1.2. Phm v ng dng ca mang nron nhn to ............................................. 20

1.2.1. Nhng bi ton thch hp .................................................................... 20

1.2.1.1. Phn loi ........................................................................................ 21

1.2.1.2. M hnh ho .................................................................................. 21


iv

1.2.1.3. Bin i .......................................................................................... 23

1.2.1.4. Lin kt ......................................................................................... 23

1.2.2. Cc lnh vc ng dng mng nron ..................................................... 24

1.3. Mng KOHONEN .................................................................................. 26

1.3.1. Gii thiu v mng Nron Kohonen .................................................... 26

1.3.2. Cu trc ca mng nron Kohonen [9] ................................................ 27

1.3.3. Thc hin mng nron Kohonen [9] .................................................... 28

1.3.3.1 Chun ha u vo .......................................................................... 28

1.3.3.2 Tnh ton u ra cho mi nron...................................................... 29

1.3.3.3 Chn nron chin thng .................................................................. 29

1.3.3.4 Qu trnh hc ca mng nron Kohonen ........................................ 30

1.3.3.4.1 Tc hc ................................................................................ 32

1.3.3.4.2 Hiu chnh trng s .................................................................. 33

1.3.3.4.3 Tnh ton li ............................................................................. 34

CHNG II .......................................................................................................... 36

NG DNG MNG NRON KOHONEN TRONG BI TON NHN DNG

CH VIT TAY TING VIT ............................................................................ 36

2.1. Tng quan v bi ton nhn dng ............................................................ 36

2.2. Gii thiu v bi ton nhn dng ch vit tay Ting Vit .......................... 39

2.3. Phng php nhn dng ch vit tay s dng mng nron ....................... 43

2.4. Pht biu bi ton ........................................................................................ 44

2.5 Cc bc gii quyt bi ton s dng mng nron Kohonen ..................... 44

2.5.1.Xy dng giao din v .......................................................................... 44

2.5.2. Xy dng mng nron Kohonen .......................................................... 47

2.5.3. X l d liu (phn tch nh) .............................................................. 47


v

2.5.4. Hun luyn mng nron Kohonen ....................................................... 48

2.5.5 Nhn dng mng nron Kohonen ......................................................... 50

2.5.6 Kt lun ................................................................................................. 50

CHNG III ......................................................................................................... 52

M PHNG NHN DNG K T VlT TAY TING VIT RI RC S

DNG MNG NRON KOHONEN .................................................................. 52

3.1 Gii thiu ..................................................................................................... 52

3.2 Thc hin chng trnh nhn dng k t .................................................... 53

3.2.1 Xc nh cc tham s cho mng ............................................................ 54

3.2.2 V hnh nh ........................................................................................... 55

3.2.3 Ly mu xung hnh nh ....................................................................... 56

3.2.3.1 Lu hnh nh c ly mu xung ................................................. 56

3.2.3.2 Kch thc v v tr ......................................................................... 56

3.2.3.3 Thc hin ly mu xung ............................................................... 57

3.2.4 Cc tp hun luyn ................................................................................ 58

3.2.5 Lp mng c bn ................................................................................... 58

3.2.6 Lp mng nron Kohonen .................................................................... 59

3.2.6.1 Tnh ton u ra ca mng Kohonen .............................................. 61

3.2.6.2 Hun luyn mng nron Kohonen .................................................. 62

3.3 Chng trnh m phng ............................................................................... 65

3.3.1 Cc chc nng ca chng trnh ........................................................... 65

3.3.2 Kt qu nhn dng ................................................................................. 66

3.3.3 Kt lun ................................................................................................. 68


vi

CHNG IV: KT LUN .................................................................................. 71

4.1 Cc kt qu t c ............................................................................... 71

4.1.1 V mt l thuyt .................................................................................... 71

4.1.2 V mt thc tin .................................................................................... 72

4.2 Hng pht trin tip tbeo ........................................................................... 73

4.3 Mt vi suy ngh sau khi nghin cu ........................................................... 73

TI LIU THAM KHO ..................................................................................... 75


vii

DANH MC CC T TING ANH VIT TT

STT T vit tt T vit tng minh

1 HMM Hiden Markov Model

2 LVQ Learning Vector Quantization

3 MLP Multi Layer Perception

4 OCR Optical Character Recognation

5 PDA Personal Digital Assistant

6 RFID Radio Frequency Identification

7 SOM Self Organizing Maps

8 SVM Support Vector Machine


viii

DANH MC CC HNH

Hnh 1.1. M hnh n-ron sinh hc ......................................................................... 6

th hm ng nht (Identity function) ............................................................... 8

th hm bc nh phn (Binary step function) .................................................. 9

th hm sigmoid ............................................................................................... 10

th hm sigmoid lng cc .............................................................................. 10

Hnh 1.2. M hnh mt n-ron .............................................................................. 11

Hnh 1.3. Mng truyn thng mt lp ................................................................... 14

Hnh 1.4. Mng truyn thng nhiu lp ................................................................ 15

Hnh 1.5. Mng mt lp c ni ngc .................................................................. 16

Hnh 1.6. Mng nhiu lp c ni ngc ............................................................... 16

Hnh 1.7: Cu trc ca mng Kohonen ................................................................. 27

Hnh 1.8: Mng nron Kohonen in hnh ........................................................... 28

Hnh 1.9: Hun luyn mng Kohonen (SOM) ..................................................... 30

Hnh 1.10. Qu trnh hun luyn mng nron Kohonen ....................................... 31

Hnh 2.1: M hnh chung trong nhn dng ch vit ............................................. 42

Hnh 2.2: Qu trnh tm gii hn k t .................................................................. 45

Hnh 2.3: Qu trnh ly mu xung ....................................................................... 45

Hnh 2.4 Qu trnh nh x t ma trn im sang ma trn gi tr .......................... 48

Hnh 2.5 Qu trnh hun luyn mng nron Kohonen .......................................... 49

Hnh 3.1 Giao din chng trnh m phng ......................................................... 65

Hnh 3.2 Nhn dng k t ................................................................................. 67

Hnh 3.3 Nhn dng k t ................................................................................. 67

Hnh 3.4 Nhn dng k t ................................................................................. 68


ix


1

PHN M U

Trong ngnh cng ngh thng tin hin nay, tr tu nhn to hin i ang

c s quan tm rt ln. Cc my tnh v cng ngh vi in t hin i ang hy

vng cc phng php ny nh cha kha m ra th h my tnh thng minh

mi m phng c nh b no con ngi. Nghin cu v m phng tr no, c

th l t bo thn kinh (Neural) l mt c mun t lu ca nhn loi. Vi

khong 15 t Neural no ngi, mi Neural c th nhn hng vn tn hiu t

khp thn kinh v c coi l mt c ch sinh vt phc tp nht. No ngi c

kh nng gii quyt nhng vn nh: nghe, nhn, ni, hi c thng tin, phn

bit cc mu mc d s kin c b mo m, hay thiu ht. No thc hin nhng

nhim v nh vy nh cc phn t tnh ton (Neural thn kinh). No phn b

vic x l cho hng t Neural c lin quan, iu khin cc mi lin h gia cc

Neural . Neural khng ngng nhn v truyn thng tin ln nhau. C ch hot

ng ca Neural [1] bao gm: lin kt (association), tng qut ha (generation),

v t t chc (Self Orgazation). Cc Nron t lin kt vi nhau thnh mng

trong x l. Mi mng gm hng vn cc phn t Nron khc nhau. Mi phn t

Nron c kh nng lin kt vi hng nghn cc Nron khc.

Hin nay, mng Nron c a vo ng dng rng ri trong rt nhiu

lnh vc. V bi ton nhn dng l bi ton s dng cc tnh nng ca mng

Nron nhiu nht. Bi ton nhn dng vi s tr gip ca mng Nron ngy nay

khng cn dng mc nghin cu na m n tr thnh mt lnh vc p

dng vo thc t. Cc bi ton nhn dng c nghin cu nhiu nht hin nay

tp trung vo nhn dng mu hnh hc (vn tay, mt ngi, hnh khi ), nhn

dng ting ni v nhn dng ch vit. Chng c ng dng trong rt nhiu lnh


2

vc nh y hc, d bo thi tit, d bo chy rng, , cc lnh vc t ng ha

nh iu khin r-bt, iu khin cc thit b bng ging ni,. Trong s cc

bi ton nhn dng ny, nhn dng ch vit ang c ng dng rt ph bin.

Nhn dng ch vit c ng dng trong qu trnh t ng ha cc cng vic

vn phng nh nhp liu, lu tr vn bn, sch bo, phn loi th tn,, nhng

cng vic rt nhm chn v i hi nhiu thi gian ca con ngi. Nhn dng

bng mng Nron ang c ng dng trong hng lot lnh vc quan trng ca

cuc sng, phc v li ch trc tip v thit thc cho cng vic ca con ngi.

Mc ch ca lun vn l: Trnh by cc kt qu nghin cu l thuyt phc

v cho ch : Nhn dng ch vit tay Ting Vit s dng mng Nron. Tuy

nhin, do hn ch v mt thi gian cng nh phc tp ca bi ton m trong

khun kh, thi lng ca lun vn, ti ch i su nghin cu v a ra mt

chng trnh m phng nhn dng k t vit tay Ting Vit ri rc trc tuyn s

dng mng Nron Kohonen.


3

CHNG I TNG QUAN V MNG NRON NHN TO

V MNG NRON KOHONEN

1.1. Gii thiu v mng nron nhn to

1.1.1 Lch s pht trin

Khi nim mng n-ron c bt u vo cui th k 19, u th k 20 do

c s tham gia ca ba ngnh Vt l hc, Tm l hc v Thn kinh hc. Cc nh

khoa hc nh Hermann Von Hemholtz, Earnst Mach, Ivan Pavlov vi cc cng

trnh nghin cu i su vo l thuyt tng qut m t hot ng ca tr tu con

ngi nh: Hc, nhn, v lp lun, .. nhng khng a ra c m hnh ton hc

c th m t hot ng ca n-ron.

V lch s, qu trnh nghin cu v pht trin mng n-ron nhn to c th

chia thnh bn giai on nh sau:

+ Giai on mt: T nghin cu ca William (1890) v tm l hc vi s

lin kt cc n-ron thn kinh. Nm 1943, nh thn kinh hc Warren MeCulloch

v nh logic hc Walter Pitts ch ra rng:v nguyn tc mng cc n-ron nhn

to c th c m hnh ho nh thit b ngng (gii hn) thc hin tnh

ton bt k mt hm s hc hay cc php tnh logic no. Tip theo hai ng l

Donald Hebb vi gii thut hun luyn mng ra i nm 1949.

+ Giai on hai: Vo khong nhng nm 1960, mt s m hnh n-ron

hon thin hn c tnh ng dng thc tin c a ra nh: m hnh

Perceptron ca Frank Rosenblatt (1958), m hnh Adaline ca Bernard Widrow

(1962). Trong m hnh Perceptron rt c quan tm v nguyn l n gin,

nhng n cng c hn ch v nh Marvin Minsky v Seymour Papert ca MIT


4

(Massachurehs Insritute of Technology) pht hin ra v chng minh n khng

dng c cho cc hm logic phc (1969). Cn Adaline l m hnh tuyn tnh,

t chnh, c dng rng ri trong iu khin thch nghi, tch nhiu v vn pht

trin cho n nay.

+ Giai on ba: Vo khong u thp nin 80, vic nghin cu mng n-

ron din ra rt mnh m cng vi s ra i ca my tnh c nhn PC. Nhng

ng gp ln cho mng n-ron trong giai on ny phi k n Stephen

Grossberg, Teuvo Kohonen, Rumelhart v John Hopfield. Trong ng gp

ln ca nh vt l hc ngi M John Hopfield gm hai mng phn hi: Mng

ri rc nm 1982 v mng lin tc nm 1984. c bit, ng d kin nhiu kh

nng tnh ton ln ca mng m mt n-ron khng c kh nng . Cm nhn

ca Hopfield c Rumelhart, Hinton v Williams xut thut ton sai s

truyn ngc (back propagation) ni ting hun luyn mng n-ron nhiu

lp nhm gii bi ton m mng khc khng thc hin c. Nhiu ng dng

mnh m ca mng n-ron ra i cng vi cc mng theo kiu my Boltzmann

v mng Neocognition ca Fukushima.

+ Giai on bn: t nm 1987 - n nay, hng nm th gii u m hi

ngh ton cu chuyn ngnh n-ron IJCNN (International Joint Conference on

Neural Networks). Rt nhiu cng trnh c nghin cu ng dng mng n-

ron vo cc lnh vc cuc sng, v d nh: K thut tnh, ti u, sinh hc, y hc,

thng k, giao thng, ho hc Cho n nay, mng n-ron tm c v khng

nh c v tr ca mnh trong rt nhiu ng dng khc nhau.

1.1.2. M hnh mng n-ron nhn to

1.1.2.1. N-ron sinh hc


5

B no con ngi c khong 1010 t bo thn kinh lin kt cht ch vi nhau

c gi l cc n-ron. Mi n-ron gm c ba phn: Thn n-ron vi nhn bn

trong (soma), mt u si trc thn kinh ra (axon) v mt h thng t bo hnh cy

(dendrite). T bo hnh cy c nhim v mang cc tn hiu in ti cc t bo thn,

t bo thn s thc hin gp (Sum) v phn ngng ( Thresholds) cc tn hiu n.

Si trc thn kinh lm nhim v a cc tn hiu thn ra ngoi

Trong thc t c rt nhiu dy thn kinh vo v chng bao ph mt din tch

rt ln (0.25 mm2) nhn cc tn hiu t cc n-ron khc. u thn kinh ra c

r nhnh nhm chuyn giao tn hiu t thn n-ron ti n-ron khc. Cc nhnh ca

u thn kinh c ni vi cc khp thn kinh (synapse). Cc khp thn kinh ny

c ni vi thn kinh vo ca cc n-ron khc. S sp xp ca cc n-ron v mc

mnh yu ca cc khp thn kinh c quyt nh bi qu trnh ha hc phc

tp, s thit lp chc nng ca mng n-ron, cc n-ron c th sa i tn hiu ti

cc khp, trong cc n-ron nhn to c gi l trng s.

C th ni, mng n-ron sinh hc hot ng chm hn rt nhiu so vi cc

linh kin in t (10-3 giy so vi 10-9 giy), nhng b no c th thc hin nhiu

cng vic nhanh hn rt nhiu so vi my tnh thng thng. Do cu trc song song

ca mng n-ron sinh hc th hin ton b cc n-ron thc hin ng thi ti mt

thi im. Mng n-ron nhn to cng c c c im ny. Cc mng n-ron

nhn to ch yu thc nghim trn cc my tnh mnh c vi mch tch hp rt ln,

cc thit b quang, b x l song song. iu ny cng gii thch ti sao nhng

nghin cu khoa hc v mng n-ron nhn to c iu kin pht trin cng vi s

pht trin v k thut cng ngh phn cng my tnh.

C nhiu loi n-ron khc nhau v kch thc v kh nng thu pht tn hiu.

Tuy nhin, chng c cu trc v nguyn l hot ng chung.


6

Hnh v (1.1) l mt hnh nh n gin ho ca mt loi n-ron nh vy.

Hnh 1.1. M hnh n-ron sinh hc

- Hot ng ca n-ron sinh hc c th m t tm tt nh sau:

Mi n-ron nhn tn hiu vo t cc t bo thn kinh khc.Chng tch hp

cc tn hiu vo, khi tng tn hiu vt qu mt ngng no chng to tn

hiu ra v gi tn hiu ny ti cc n-ron khc thng qua dy thn kinh. Cc n-

ron lin kt vi nhau thnh mng. Mc bn vng ca cc lin kt ny xc

nh mt h s gi l trng s lin kt.

1.1.2.2. N-ron nhn to

m phng cc t bo thn kinh v cc khp ni thn kinh ca b no

con ngi, mng n-ron nhn to c cc thnh phn c vai tr tng t l cc

n-ron nhn to v kt ni gia chng (kt ni ny gi l weights). N-ron l

mt n v tnh ton c nhiu u vo v mt u ra, mi u vo n t mt

khp ni thn kinh (synapse). c trng ca n-ron l mt hm kch hot phi

tuyn chuyn i mt t hp tuyn tnh ca tt c cc tn hiu u vo thnh tn

hiu u ra.


7

Mt n-ron nhn to l mt n v tnh ton hay n v x l thng tin c

s cho hot ng ca mt mng n-ron.

Cc thnh phn c bn ca mt m hnh n-ron

Trng s v tng tn hiu u vo:

Mi n-ron c rt nhiu dy thn kinh vo, ngha l mi n-ron c th tip

nhn ng thi nhiu tn hiu. Gi s ti n-ron i c N tn hiu vo, mi tn hiu

vo jS c gn mt trng s ijW tng ng. Ta c lng tng tn hiu i vo

n-ron inet theo mt s dng sau:

(i)Dng tuyn tnh:

1

N

i ij j

j

net W s

(1.1)

(ii)Dng ton phng:

2

1

N

i ij j

j

net W s

(1.2)

(iii)Dng mt cu:

2

2

ij

1

wN

i j

j

net s

(1.3)

Trong : v ijw 1,j N ln lt l tm v bn knh mt cu


8

Hm kch hot (hm chuyn):

Hu ht cc n v trong mng n-ron chuyn net input bng cch s dng

mt hm v hng (scalar to scalar function) gi l hm kch hot, kt qu

ca hm ny l mt gi tr gi l mc kch hot ca n v. Tr kh nng n

v thuc lp ra, gi tr kch hot c a vo mt hay nhiu n v khc. Cc

hm kch hot thng b p vo mt khong gi tr xc nh, do thng c

gi l cc hm nn (squashing).

Hm bin i tn hiu u vo net cho tn hiu u ra out c gi l hm

kch hot. Hm ny c c im l khng m v b chn, dng gii hn bin

u ra ca n-ron. C nhiu dng hm kch hot, ngi ta thng s dng mt hm

kch hot chung cho ton mng.

Mt s hm kch hot thng c s dng:

1) Hm ng nht (Linear function, Identity function)

g(x) = x (1.4)

Nu coi cc u vo l mt n v th chng s s dng hm ny. C khi mt

hng s c nhn vi net-input to thnh mt hm ng nht.

th hm ng nht (Identity function)

2) Hm bc nh phn (Binary step function, Hard limit function)


9

Hm ny cn gi l hm ngng (Threshold function hay Heaviside

function). u ra ca hm ny gii hn mt trong hai gi tr:

1,

( )

0,

neu xg x

neu x

(1.5)

y l ngng.

th hm bc nh phn (Binary step function)

Dng hm ny thng s dng trong mng mt lp. Trong hnh v c chn

bng 1.

3) Hm sigmoid (Sigmoid function (logsig))

Hm sigma l dng chung nht ca hm kch hot c s dng trong cu

trc mng n-ron nhn to. N l mt hm tng v n th hin mt s trung gian

gia tuyn tnh v phi tuyn. Mt v d ca hm ny l hm logistics, xc nh

nh sau:

1

( )

1x

g x

e

(1.6)

l tham s dc ca hm sigma. Bng vic bin i tham s , chng

ta thu c cc hm sigma vi cc dc khc nhau. Thc t, h s gc ti x= 0

l /4. Khi tham s h s gc tin ti khng xc nh, hm sigma tr thnh mt

hm ngng n gin. Trong khi mt hm ngng ch c gi tr l 0 hoc 1, th


10

mt hm sigma nhn cc gi tr t 0 ti 1. Cng phi ghi nhn rng hm sigma l

hm phn bit, trong khi hm ngng th khng (Tnh phn bit ca hm l mt

c tnh quan trng trong l thuyt mng neuron). Hm ny thng c dng

cho cc mng c hun luyn (trained) bi thut ton lan truyn ngc (back

propagation), bi n d ly o hm, lm gim ng k tnh ton trong qu trnh

hun luyn. Hm c dng cho cc chng trnh ng dng m u ra mong

mun ri vo khong [0,1].

th hm sigmoid

4) Hm sigmoid lng cc (Bipolar sigmoid function (tan(sig))

1

( )

1

x

x

eg x

e

(1.7)

Hm ny c c tnh tng t hm sigmoid. Hm lm vic tt i vi cc ng

dng c u ra yu cu trong khong [-1,1].

th hm sigmoid lng cc


11

Cc hm chuyn ca cc n v n (hidden units) l cn thit biu din s

phi tuyn vo trong mng.

Nt bias:

L mt nt thm vo nhm tng kh nng thch nghi ca mng n-ron

trong qu trnh hc. Trong cc mng n-ron c s dng bias, mi n-ron c th

c mt trng s tng ng vi bias. Trng s ny lun c gi tr l 1.

M hnh ca mt nt x l (nt th i):

Hnh 1.2. M hnh mt n-ron

N

ijj

ijiji VWU

#1

(1.8)

iii UfV (1.9)

Trong :

iU : l tn hiu vo ti n-ron i

iV : l tn hiu ra ti nron i

ijW : l trng s lin k t n-ron j n n-ron i

Vi=fi(Ui) Ui= Vi

Vi

Wi1

Vj

VN

Wij

WiN


12

i: l ngng (u vo ngoi) kch hot n-ron i.

if : l hm kch hot ca n-ron i

1.1.2.3. Mng n-ron nhn to

Mng n-ron nhn to (gi tt l mng n-ron) l m hnh ton hc hay

m hnh tnh ton c xy dng da trn cc mng n-ron sinh hc. N gm c

mt nhm cc n-ron nhn to(nt) ni vi nhau, v x l thng tin bng cch

truyn theo cc kt ni v tnh gi tr mi ti cc nt (cch tip cn

connectionism i vi tnh ton). Phn ln mng n-ron nhn to l mt h

thng thch ng (adaptive system) t thay i cu trc ca mnh da trn cc

thng tin bn ngoi hay bn trong chy qua mng trong qu trnh hc.

Vi vic gi lp cc h thng sinh hc, cc cu trc tnh ton, mng n-

ron c th gii quyt c cc lp bi ton nht nh, nh: Bi ton ngi du

lch, bi ton t mu bn , bi ton xp loi, bi ton lp thi kha biu, bi

ton tm kim, bi ton nhn dng mu... Cc bi ton phc tp cao, khng xc

nh. Tuy nhin, s lin kt gia mt bi ton bt k trong thc t vi mt gii

php mng n-ron li l mt vic khng d dng.

Xt mt cch tng qut, mng n-ron l mt cu trc x l song song

thng tin phn tn mang cc c tnh ni bt sau :

L m hnh ton hc da trn bn cht ca n-ron.

Bao gm mt s lng rt ln cc n-ron lin kt vi nhau.

Mng n-ron c kh nng hc, khi qut ha tp d liu hc thng

qua vic gn v hiu chnh cc trng s lin kt.


13

T chc theo kiu tp hp mang li cho mng n-ron kh nng tnh

ton rt ln, trong khng c n-ron no mang thng tin ring

bit.

V d : Hnh 1.2, 1.3,1.4, 1.5 l mt s m hnh mng thng dng.

Cc hnh trng ca mng

Hnh trng mng c nh ngha bi: s lp (layers), s n v trn mi

lp, v s lin kt gia cc lp . Cc mng thng c chia lm hai loi da

trn cch thc lin kt cc n v:

1.1.2.3.1. Mng truyn thng

- Mng truyn thng mt lp

Mng perceptron mt lp do F.Rosenblatt xut nm 1960 l mng

truyn thng ch mt lp vo v mt lp ra khng c lp n. Trn mi lp ny c

th c mt hoc nhiu n-ron. M hnh mng n-ron ca F.Rosenblatt s dng

hm ngng ng vai tr l hm chuyn. Do , tng ca tn hiu vo ln hn

gi tr ngng th gi tr u ra ca n-ron s l 1, cn tri li s l 0.

1,

0,

i

i

i

neu netout

neu net

(1.10)

Vi neti = wij jx l tng thng tin u vo ca n-ron i.

M hnh mng n-ron truyn thng mt lp l m hnh lin kt c bn v

n gin nht. Cc n-ron t chc li vi nhau to thnh mt lp, ng truyn

tn hiu c truyn theo mt hng nht nh no . Cc u vo c ni vi

cc n-ron theo cc trng s khc nhau, sau qu trnh x l cho ra mt chui cc

tn hiu ra.


14

TiniiT

i wwwW ,...,, 21

Hnh 1.3. Mng truyn thng mt lp

Vi mi gi tr u vo. . Qua qu trnh x l ca

mng ta s thu c mt b tng ng cc gi tr u ra l

c xc nh nh sau :

Trong :

m : S tn hiu vo

n : S tn hiu ra

: l vc t trng s ca n-ron th i.

if : L hm kch hot n-ron th i

i : L ngng ca n-ron th i.

Ngay t khi mng Perceptron c xut n c s dng gii quyt bi

ton phn lp. Mt i tng s c n-ron i phn vo lp A nu :

y1

yn

y2

Xm

x1

x2

Tnyyyy ...,,2,1

nixwfym

j

ijijii ,1,1

(1.11)

Tnxxxx ...,,2,1


15

Tng thng tin u vo wij jx > i

Trong trng hp tri li n-ron s c phn vo lp B.

- Mng truyn thng nhiu lp (Multilayer Perceptron MLP)

Vi mng n-ron truyn thng mt lp trn, khi phn tch mt bi ton

phc tp s gp rt nhiu kh khn, khc phc vn ny ngi ta a ra m

hnh mng n-ron truyn thng nhiu lp bng vic kt hp mt s lp n-ron li

vi nhau. Lp nhn tn hiu vo gi l lp vo, lp a tn hiu ra ca mng

c gi l lp ra. Cc lp gia lp vo v lp ra c gi l lp n v cc n-

ron trong cc lp n c hm chuyn (hm kch hot) dng phi tuyn. Mng n-

ron nhiu lp c th gii quyt cc bi ton phi tuyn nh vo cc lp n. Cng

nhiu lp n th kh nng m rng thng tin cng cao v x l tt mng c nhiu

lp vo v lp ra.

Hnh (1.4) m t cu trc ca mng n-ron truyn thng nhiu lp.

Hnh 1.4. Mng truyn thng nhiu lp

1.1.2.3.2. Mng hi quy (Recurrent Neutral Network)

Mng hi quy mt lp c phn hi

y1

yn

y2

xm

x1

x2

Lp vo Lp ra Lp n


16

Hnh 1.5. Mng mt lp c phn hi

Mng hi quy nhiu lp c phn hi.

Hnh 1.6. Mng nhiu lp c phn hi

1.1.2.4. Lut hc

Tin trnh hc l tin trnh quan trng ca con ngi, nh hc m b no

ngy cng tch ly cc kinh nghim thch nghi vi mi trng v x l tnh

hung tt hn. Mng n-ron xy dng li cu trc b no th phi cn c kh

nng nhn bit d liu thng qua tin trnh hc, vi cc thng s t do ca mng

c th thay i lin tc bi nhng thay i ca mi trng v mng n-ron ghi

nh gi tr .

. . . . . . . . .

X1

X2

XN

Y1

Y2

YM

Y1

Y2

Y

M

. . . . . .

X1

X2

XN

. . . . . .


17

Trong qu trnh hc, gi tr u vo c a vo mng v theo dng chy

trong mng to thnh gi tr u ra.

Tip n l qu trnh so snh gi tr to ra bi mng n-ron vi gi tr

mong mun. Nu hai gi tr ny ging nhau th khng thay i g c. Tuy nhin,

nu c mt sai lch gia hai gi tr ny vt qu gi tr sai s mong mun th i

ngc mng t u ra v u vo thay i mt s kt ni.

y l qu trnh lp li lin tc v c th khng dng khi khng tm c

gi tr W sao cho u ra to bi mng n-ron bng ng u ra mong mun. Do

trong thc t ngi ta phi thit lp mt s tiu chun da trn mt gi tr sai

s no ca hai gi tr ny, hay da trn mt s ln lp nht nh.

tin cho vic trnh by, ta k hiu y l gi tr kt xut ca mng n-ron,

t l gi tr ra mong mun, e l sai lch gia hai gi tr ny.:

e = t - y

Mng n-ron c mt s u im so vi my tnh truyn thng. Cu trc

song song ca mng n-ron rt thch hp cho nhng ng dng i hi tc

nhanh theo thi gian thc. Kh nng hun luyn ca mng n-ron c th khai

thc pht trin h thng thch nghi. Mt khc, vi kh nng tng qut ha ca

mng n-ron, n c th p dng iu khin nhiu tham s phc tp ng thi

t gii quyt d dng mt s bi ton thuc lp bi ton NP- y (NP-

Complete ).

Cc lut hc ng vai tr quan trng trong vic xc nh mt mng n-

ron nhn to. Mt cch n gin v khi nim hc ca mng n-ron l cp nht

trng s trn c s cc mu. Theo ngha rng th hc c th c chia ra lm hai

loi: Hc tham s v hc cu trc.


18

- Hc tham s: Cc th tc hc ny nhm tm kim ma trn trng s sao

cho mng c kh nng a ra d bo st vi thc t. Dng chung ca lut hc

tham s c th c m t nh sau:

trong :

ijW : l s thay i trng s lin kt t nron j n nron i.

jx : l tn hiu vo t nron j.

: l tc hc, nm trong khong (0,1).

r : l hng s hc.

Vn t ra y l tn hiu hc r c sinh ra nh th no hiu

chnh trng s ca mng.

C th chia th tc hc tham s ra thnh ba lp hc nh hn: Hc c ch

o, hc tng cng v hc khng ch o. Vic xc nh r ty thuc vo tng

kiu hc.

+ Hc c tn hiu ch o: L qu trnh mng hc da vo sai s gia u

ra thc v u ra mong mun lm c s cho vic hiu chnh trng s. Sai s

ny chnh l hng s hc r. Lut hc in hnh ca nhm ny l lut hc Delta

ca Widrow (1962) nu ra u tin dng xp x trng ca Adaline da trn

nguyn tc gim gradient.

Trong nhm lut hc ny cng cn phi k n lut hc Perceptron ca

Rosenblatt (1958). V c bn lut hc ny thay i cc gi tr trng trong thi

gian hc, cn lut Perceptron th thm hoc b trng ty theo gi tr sai s dng

hay m.

MjNirxW jij ,1,,1, (1.12)


19

Mt lot cc lut hc khc cng c da trn t tng ny. Lut Oja l

ci tin v nng cp ca lut Delta. Lut truyn ngc l lut m rng ca lut

Delta cho mng nhiu lp. i vi mng truyn thng thng s dng lut

truyn ngc chnh trng vi tn hiu ch o t bn ngoi v ngi ta gi

mng ny l mng lan truyn ngc.

+ Hc khng c tn hiu ch o: Lut hc ny s dng u ra ca mng

lm c s hiu chnh cc trng s lin kt. Hay trong lut ny chnh l tn hiu

ra ca mng. in hnh l lut Hebb (1949) thng dng cho cc mng t lin

kt, lut LVQ (Learning Vector Quantization) dng cho mng t t chc mt lp

thuc lp mng nh x c trng ca Kohonen.

Lut hc Hebb l lut sinh hc xut pht t tin ca Hebb cho rng:

Gia hai n-ron c quan h v c thay i th nng th gia chng c s thay i

trng s lin kt. Ni cch khc, trng s c iu chnh theo mi tng quan

trc v sau, ngha l:

trong :

ijW l s thay i trng s lin kt t n-ron j n n-ron i.

:jx l tn hiu vo n-ron j.

iy l tn hiu ra ca n-ron i.

l tc hc, nm trong khong (0,1).

Lut Hebb gii thch vic chnh trng trong phm vi cc b ca mng m

khng cn tn hiu ch o t bn ngoi. Hopfield cng ci tin lut Hebb cho

MjNixyW jiij ,1,,1, (1.13)


20

cc mng t lin kt thnh 16 dng khc nhau theo kiu lut Hebb, lut i

Hebb, lut Hopfield...

Nh vy, ng vi mi nhm mng thng p dng mt lut hc nht nh.

Nu tn ti hng chc loi mng khc nhau th cc lut hc dng trong mng n-

ron c th tng ln rt nhiu ln.

i vi mng phn hi thng s dng lut Hebb v cc lut ci tin ca

n chnh trng m khng cn tn hiu ch o t bn ngoi.

+ Hc tng cng: Trong mt s trng hp, thng tin phn hi ch l tn

hiu bao gm hai trng thi cho bit tn hiu u ra ca mng l ng hay sai.

Qu trnh hc da trn cc thng tin hng dn nh vy c gi l hc c cng

c (hc tng cng) v tn hiu mang thng tin phn hi c gi l tn hiu

cng c cho qu trnh hc. Ta c th thy rng qu trnh hc ny l mt dng ca

qu trnh hc c tn hiu ch o bi v mng nhn c mt s thng tin phn

hi t bn ngoi.

- Hc cu trc: Tm kim cc tham s ca cu trc mng tm ra mt cu

trc mng hot ng tt nht. Trong thc t, vic hc cu trc l tm ra s lp n

v tm ra s n-ron trn mi lp . Gii thut di truyn thng c s dng

trong cc cu trc nhng thng chy rt lu, thm ch ngay c i vi mng c

kch thc trung bnh. Ngoi ra k thut gt ta mng hay mng tng dn cng

c p dng trong vic hc cu trc ca mng c kch thc tng i nh.

1.2. Phm v ng dng ca mang nron nhn to

1.2.1. Nhng bi ton thch hp

Mng nron c coi nh l hp en bin i vc-t u vo m bin

thnh vct u ra n bin. Tn hiu ra c th l cc tham s thc, (tt nht nm


21

trong khong [0, 1], hoc [-1, 1]), s nh phn 0, 1, hay s lng cc -1;+1. S

bin ca vc-t vo ra khng b hn ch xong s nh hng ti thi gian tnh v

ti d liu ca my tnh. Ni chung, cc lp bi ton p dng cho n-ron c th

c phn chia thnh bn loi:

1. Phn lp (classification).

2. M hnh ho (modeling).

3. Bin i, thc hin nh x t mt khng gian a bin vo khng gian a

bin khc tng ng (transformation and mapping).

4. Lin kt v k thut dch chuyn ca s (association and moving

window).

1.2.1.1. Phn loi

Mt trong cc cng vic n gin v thng c s dng nhiu trong

vic qun l cc i tng a bin l phn loi (phn lp mt i tng vo cc

nhm, nhm con, hay chng loi). V d: Bi ton phn lp nh, nhn dng mu,

. . .

Khi phi phn loi mt quyt nh phc tp, chng ta phi bt u vi

vic nghin cu thng k cc mi lin quan gia nhiu i tng v thuc tnh

ca lp cc i tng. C th ni vic xy dng mt cy phn lp cc quyt nh

phi c thc hin trc khi th tc hc c tin hnh. Nu kt qu cui cng

khng tho mn, chng ta cn phi xem xt li cch biu din cc i tng hoc

cy phn lp hoc thay i c hai.

1.2.1.2. M hnh ho

Cc h thng phn loi a ra cc cu tr li ri rc nh c, khng hoc

mt s nguyn nh danh cc i tng u vo thuc lp no. M hnh ho yu


22

cu h thng phi sn sinh ra cc cu tr li mang tnh lin tc. Trong qu trnh

m hnh ho, cn mt s lng nh cc s liu xy dng m hnh.

M hnh ny c th a ra cc d bo cho tt c cc i tng u vo.

Vic tm ra ng cong ph hp vi cc s liu thc nghim l mt trong nhng

ng dng thuc dng ny. Trong bt k loi m hnh no cng phi tun theo

mt gi nh l: cc thay i nh ca tn hiu vo ch gy ra nhng bin i nh

ca tn hiu ra.

Trong cc vn a bin, mng n-ron c nhiu li th hn so vi cc

phng php m hnh ho c in s dng cc hm gii tch. Bi v trong

phng php m hnh ho c in i vi mi u ra, ta phi nh ngha mt

hm c th cng mt b cc tham s, trong khi i vi mng n-ron th khng

phi quan tm ti cc hm . Tuy nhin, trong cc phng php m hnh ho c

in, cc h s c th c mt s ngha no i vi vn cn gii quyt, tri

li cc trng s ca mng khng mang mt ngha no c.

Trong nhiu ng dng kh c bit, khi sai s thc hin kh ln chng ta

c th m hnh ho bng cch cn xng ho gia tn hiu vo tn hiu ra. Trong

cc trng hp ny, s dng mng nh mt bng tra l , mc d cc bng ny

s cho li gii ging nhau trong mt khong no ca tn hiu vo.

i vi vic chn chin lc hc, chng ta cn quan tm n s phn b

ca cc i tng dng hc. Nu s lng i tng dng cho vic hc l t

v c phn b tng i u trong ton khng gian, khi s liu c th c

dng ngay cho vic m hnh ho. Tri li, nu cc i tng l nhiu, sn c

nhng phn b ngu nhin trong khng gian bin, u tin phi gim thiu chng


23

sao cho vn bao trm ton khng gian, sau mi dng lm s liu cho vic m

hnh ho.

1.2.1.3. Bin i

Vic bin i nhm mc ch nn cc i tng t khng gian m chiu

vo khng gian c s chiu nh hn rt nhiu. Qua vic nn, cc i tng ny s

bc l cc c im m chng ta khng th nhn thy khi chng thuc khng gian

nhiu chiu. Theo mt chng mc no , bin i tng t nh vic nhm cc

i tng hay phn loi th hin ch biu din cc kt qu ra. Trong phn loi,

chng ta mun nh danh cc nhm hoc lp m i tng thuc vo, cn trong

bin i, chng ta quan tm n ton b cc i tng v t chng ta thu nhn

c cc nhm t cc i tng hc. im quan trng trong bin i l cc i

tng c biu din bi to ca n-ron trung tm ch khng phi l gi tr

ca tn hiu ra.

Mt trong nhng ng dng ca vic bin i l tin x l (thng c

gi l k hoch ho thc nghim). Thng qua qu trnh tin x l, chng ta c th

chn ra cc i tng in hnh t tp v s cc i tng ngu nhin, loi tr

cc i tng d tha hay trng lp. iu ny l cc k quan trng khi la chn

cc i tng lm mu hc cho mng lan truyn ngc sai s.

1.2.1.4. Lin kt

Lin kt l tm ra i tng ch c mi quan h vi mt i tng vo,

thm ch c khi i tng vo b hng hoc hon ton khng bit. Theo mt

ngha no , lin kt c th c coi l phn loi. Th tc hc cho vn ny l

hc c tn hiu ch o.


24

Lnh vc nghin cu cc qu trnh ph thuc thi gian l mt trong nhng

lnh vc chnh trong nghin cu qu trnh iu khin. y ngi s dng d

bo c cc hnh vi ca h thng a bin da trn mt chui s liu c ghi

nhn theo thi gian. Trong m hnh ho ph thuc thi gian, cc bin ca tn

hiu vo bao gm cc gi tr hin ti v qu kh ca cc bin qu trnh, trong

tn hiu ra d bo gi tr trong tng lai ca nhng bin qu trnh . V nguyn

tc cc hiu bit ny c th c cc di tu , nhng trong qu trnh kim sot

hiu bit tng lai ch bao gm mt bc thi gian. Vic hc dch chuyn ti

bc tip theo to ra cc ca s bao gm s bc thi gian ca vc-t ra. to

ra m hnh hon chnh ca mt qu trnh, tt c cc bin qu trnh phi c

hun luyn ti u ra ca mng, nhng khng phi tt c cc bin trong qu trnh

u nh hng nh nhau i vi kt qu cui cng, ch c mt s bin l ng

quan tm. Do chng ta ch phi chn cc bin cho qu trnh hc. K thut

dch chuyn ca s c th c s dng gii quyt cc vn chui cc s

kin v i tng nh trong cc lnh vc v mi trng theo thi gian, kim sot

hng hc.

1.2.2. Cc lnh vc ng dng mng nron

Trong qu trnh pht trin, mng nron c ng dng thnh cng trong

rt nhiu lnh vc. Mt s ng dng chnh ca mng n-ron c th lit k l:

- X l nh: Gm trng khp nh, tin x l nh, phn on v phn tch

nh, nn nh, ...

- X l tn hiu: phn tch tn hiu a chn v hnh thi hc.


25

- Nhn dng mu: Gm vic tch cc nt c bit ca mu, phn loi v

phn tch tn hiu ca ra a, nhn dng v hiu ting ni, nhn dng vn

tay, k t, ch vit, ..

- Y hc: phn tch v hiu tn hiu in tm , chun on bnh, x l nh

y hc.

- Cc h thng qun s: pht hin thy li, phn loi lung ra a, nhn dng

ngi ni.

- Gii tr: Hot hnh, cc hiu ng c bit, d bo th trng.

- Cc h ti chnh: Gm phn tch th trng chng khon, nh gi bt

ng sn, cho vay, kim tra ti sn cm c, nh gi mc hp tc, phn

tch ng tn dng, cp pht th tn dng, d bo t gi tin t v thng

mi an ton.

- Tr tu nhn to: Gm cc h chuyn gia, ..

- Cc h thng nng lng.

- D on: D on cc trng thi ca h thng,..

- Vn lp k hoch, iu khin v tm kim: Gm ci t song song cc

bi ton tha mn rng buc, bi ton lp thi kha biu cho trng i

hc, bi ton ngi i du lch, ..

- Gii cc bi ton ti u: Vn chnh l tm nhng thut ton hun luyn

mng gp phn tm nghim cho nhiu lp bi ton ti u ton cc.

Tm li, mng n-ron nhn to c xem l mt cch tip cn y tim nng

gii quyt cc bi ton c tnh phi tuyn, phc tp v c bit trong tnh hnh

cc d liu u vo khng tng minh.


26

1.3. Mng KOHONEN

1.3.1. Gii thiu v mng Nron Kohonen

Trong phn trc chng ta nghin cu mt s loi mng nron. Trong khi

mng nron truyn thng rt ph bin th mt cu trc mng khc cng rt ph

bin l mng Kohonen.

Mng Nron Kohonen (hay cn gi l SOM (Self-Organizing Maps) - Bn

t t chc) l mt trong nhiu loi mng thng minh nhn to (AI) do c gio s,

tin s Teuvo Kohonen xng vo nhng nm 70 ca th k trc. ng l

mt trong nhng nh nghin cu ni ting v c nhiu cng trnh trong lnh vc

tnh ton nron.

Thng thng, mng nron Kohonen gm mt lp u vo v lp u ra.

Mng ny c t tn bi tn ngi lp ra n, c gio s, tin s T. Kohonen.

Mng Kohonen khc bit so vi mng nron lan truyn ngc dn tin cch

hun luyn v cch n nh li mt m hnh. Mng Kohonen khng s dng mt

loi hm kch hot no. Xa hn l n khng s dng loi trng s bias no.

u ra ca mng Kohonen khng bao gm u ra ca mt s nron. Khi c

mt mu c a vo mng th ch c mt nron u ra c la chn gi l

nron chin thng. Nron chin thng ny chnh l u ra ca mng Kohonen.

Thng thng th cc nron chin thng ny i din cho cc nhm d liu a

vo mng Kohonen.

im khc bit quan trng nht gia mng Kohonen va mng nron truyn

thng lan truyn ngc l mng nron Kohonen hc theo phng php hc

khng gim st, c ngha l mng nron Kohonen thao tc vi d liu nhng

u ra chnh xc tng ng vi d liu vo khng c ch nh trc. S dng

mng nron Kohonen, d liu c th c phn thnh cc nhm.


27

Mng nron Kohonen c s dng bi v n l mt mng tng i n

gin v cu trc, v c th hun luyn rt nhanh.

1.3.2. Cu trc ca mng nron Kohonen [9]

Thng thng, mng nron Kohonen gm mt lp u vo v mt lp u ra.

u tin chng ta xt v u vo v u ra ca mng.

Cc nron u vo ch n gin cung cp d liu vo cho mng ch khng c

chc nng x l g trn y. i vi mng nron Kohonen yu cu u vo c

chun ha c gi tr trong phm vi t -1 n +1.

u ra ca mng Kohonen khng bao gm u ra ca mt s nron. i vi

mng nron truyn thng, nu c nm nron u vo th mt u ra bao gm

nm gi tr. Cn mng nron Kohonen khi c mt mu c a vo mng th

ch c mt nron u ra c la chn gi l nron chin thng. Nron chin

thng ny chnh l u ra ca mng nron Kohonen. u ra ca mng nron

Kohonen thng l ch s ca nron chin thng, v d Nron #5. Thng thng

th cc nron chin thng ny i din cho cc nhm d liu a vo mng

Kohonen. Cu trc ca mt mng nron Kohonen c cho nh hnh 1.7:

Hnh 1.7: Cu trc ca mng Kohonen


28

Hnh 1.8 di y l mt mng Kohonen in hnh.

Hnh 1.8: Mng nron Kohonen in hnh

1.3.3. Thc hin mng nron Kohonen [9]

1.3.3.1 Chun ha u vo

Mng Kohonen yu cu u vo c chun ha. D liu u vo nn c gi

tr nm trong khong -1 n 1. Nu mt hoc nhiu hn nron u vo s dng

cc gi tr ch nm trong khong t 0 n 1 th mng nron hot ng khng m

bo cht lng, chun ha u vo, vic u tin chng ta phi tnh chiu di

vct ca d liu u vo:

length(x) =

N

i 1

x 2i (1.14)

S dng chiu di vct, chng ta c th quyt nh h s chun ha:

N

i

ix1

2

1

(1.15)


29

1.3.3.2 Tnh ton u ra cho mi nron

tnh ton u ra cho mi vct u vo th phi cng xem xt vct u

vo v trng s. u tin phi tnh tch v hng ca cc nron u vo v cc

trng s kt ni. Tch v hng c tnh bng cch nhn mi phn t trong hai

vct vi nhau. Ta tnh tng ca tch cc phn t ca vct trng s v vct u

vo. Gi s u vo l: X= {x1, x2, ... ,xN}, trng s l W={wjl, wj2, ... , wjN} th

tch v hng ca X v W l:

t = ji

N

i

i wx1

(1.16)

Xt u ra ca nron th j by gi c chun ha bng cch nhn gi tr va

tnh c vi h s chun ha c xc nh trn.

output(j) = ( ji

N

i

iwx1

)

N

i

ix1

2

1 (1.17)

Gi tr va c tnh ton phi c nh x thnh s lng cc. nh x,

chng ta thm 1 va chia cho 2, ta c:

output(j) = [output(j) + 1] * 0.5 (1.18)

1.3.3.3 Chn nron chin thng

Khi tnh ton c u ra vi tng nron, tin hnh so snh chng tm

xem nron no c u ra ln nht (khong cch nh nht) th nron c

quyt nh l nron chin thng. Nh vy ta tm ra u ra ca mng nron

Kohonen. Ta thy gi tr ny c quyt nh bi gi tr trng s gia u vo v


30

u ra. Nh vy ta iu chnh trng s ny iu chnh gi tr u ra theo nh

nhim v yu cu.

1.3.3.4 Qu trnh hc ca mng nron Kohonen

Qu trnh hc l qu trnh hiu chnh trng s. Ton b qu trnh hun luyn

cho mng nron Kohonen bao gm cc chu k lp li cho n khi mc 1i ca

mng di mt mc chp nhn c. Qu trnh hun luyn cho mng l cnh

tranh. Vi mi tp u vo s tm c mt nron chin thng. Trng s ca

nron chin thng s c hiu chnh, n s tc ng tr li mnh m hn i

vi u vo ln tip theo. Cc nron chin thng l khc nhau i vi cc mu

khc nhau. Kh nng nhn dng cc mu ring bit ca chng s c tng ln.

u tin chng ta xt tng quan qu trnh hun luyn cho mng nron Kohonen.

Hnh 1.9: Hun luyn mng Kohonen (SOM)


31

Hnh 1.10. Qu trnh hun luyn mng nron Kohonen


32

u tin, ma trn trng s c khi to vi cc gi tr ngu nhin, a tp

mu vo v tnh ton t l li, hiu chnh trng s ca nron chin thng:

- Nu t l li c ci thin ng k th quay tr li tip tc a mu hun

luyn vo v iu chnh trng s ca nron chin thng ri tnh ton li t l li

xem mc ci thin ca n nh th no.

- Nu t l li ch ci thin rt nh th chu k ny s c b qua. Nu iu

ny xy ra th xt xem ma trn trng s ny c tt hn ma trn trng s tt nht

t trc n gi khng?

+ Nu tt hn th lu li ma trn trng s tt nht.

+ Nu khng, ma trn trng s tt nht c gi nguyn t chu k trc.

- Sau ma trn trng s c khi to li vi gi tr ngu nhin v chu k

hun luyn mi c bt u. Chu k hun luyn mi ny li tip tc ging nh

chu k trc v s phn tch cc thi k quyt nh b qua hay to ra tp

trng s m to ra mc li chp nhn c.

Nu chng ta tnh ton li nh hn mc chp nhn c hoc nu s chu k

lp ln hn s chu k lp ln nht cho php th qu trnh hun luyn hon thnh.

1.3.3.4.1 Tc hc

Tc hc l mt hng s m s c s dng trong thut ton hc. N phi

l mt s dng nh hn 1. Tc hc in hnh l 0.4, 0.5. K hiu n l .

Thng thng thit lp gi tr hc ln th qu trnh hun luyn s nhanh hn,

nhng nu thit lp gi tr ny qu ln c th lm cho mng khng bao gi hi

t. Bi v dao ng ca vct trng s qu ln phn lp mu. Mt k thut

khc nh l hun luyn tin b, qu trnh hun luyn bt u vi tc hc cao

v gim dn tc ny. Phng php ny cho php tng tc hun luyn ban

u.


33

Tc hc ch l mt bin c s dng nh mt phn ca thut ton dng

iu chnh trng s ca nron. Trong qu trnh thc nghim tin hnh iu

chnh tc hc ny sao cho ph hp t c hiu qu hun luyn cao.

1.3.3.4.2 Hiu chnh trng s

Tan b b nh ca mng nron Kohonen c lu trong trng s kt ni

gia u vo v lp u ra. Trng s c hiu chnh mi thi k. Mt thi k

xy ra khi d liu hun luyn c a vo mng v trng s c hiu chnh

da trn kt qu ca d liu hun luyn ny to ra. S iu chnh trng s lm

cho mng c c kt qu ph hp hn trong ln tip theo cng thc hin trn

cng d liu hun luyn . Nu sau mi ln a mu hun luyn vo, tnh mc

li thy c ci thin ng k th cn quay li iu chnh trng s. Cn nu khng

th bt u mt chu k mi. Khi iu ny xy ra th ton b ma trn trng s

c iu chnh n cc gi tr ngu nhin mi. Cui cng ma trn trng s s

c s dng l ma trn trng s tt nht xc nh t mi chu k. By gi chng

ta xt lm th no trng s c hiu chnh.

Phng php ban u tnh ton s thay i ca trng s, c xut bi

Kohonen, thng c gi l phng php cng vo. Phng php s dng

phng trnh sau:

(1.19)

Bin x l vct hun luyn a vo mng. Bin wt l trng s ca nron

chin thng, v wt+1 l trng s mi. th hin chiu di vct. Phng php

ny hot ng rt tt i vi mng nron Kohonen. Trong trng hp phng


34

php ny cho thy s bt n qu mc, mng khng hi t. Mt phng php

khc c s dng, phng php ny gi l phng php tr, s dng cc cng

thc sau:

(1.20)

(1.21)

Hai phng trnh ny s ch ra s bin i c bn trn trng s ca mng.

1.3.3.4.3 Tnh ton li

Trc khi chng ta hiu lm th no tnh ton li cho mng th u tin

chng ta phi hiu li c ngha l g. Mng c hun luyn theo phng php

hc khng gim st, do vy cch nh ngha v li hi khc nhau so vi cch

ngh thng thng v li. Nh cc phn khc nghin cu, hun luyn c gim

st bao gm tnh ton li, l s khc bit gia u ra tnh c v u ra

mong mun. Cn phng php hc khng gim st th khng c u ra mong

mun. Mc ch ca mng nron Kohonen l phn cc mu u vo vo cc

tp. Do li y phi c kh nng o lng mc mng phn lp tt nh

th no. Chng ta s xem xt hai phng php tnh ton li. Khng c cch

chnh thc no tnh ton li cho mng nron Kohonen. C th tnh li theo t

l phn trm, l tng cho bit mng phn loi tt nh th no i vi u

vo v cc nhm u ra. Bn thn li khng c s dng hiu chnh trng s

nh i vi thut ton lan truyn ngc. y li c xc nh bi cng tlc:

(1.22)


35

Kt lun

M hnh mng Kohonen ny tng i n gin, ch gm hai lp: lp nron

u vo v lp nron u ra. Trong , lp u vo thc ra ch dng phn b

d liu n lp nron u ra m khng c chc nng x l d liu trn . Cc

bc thc hin mng nron Kohonen tng i r rng, chi tit, n gin, d

hiu. Qu trnh hun luyn mng vi tc hi t nhanh, x l c khi lng

d liu ln.

Vic xc lp cc tham s u vo cho mng rt d dng, ta c th hiu chnh

cc tham s ny bng thc nghim trong qu trnh thc hin bi ton c th

t c kt qu hot ng tt.

Qua vic nghin cu v mng nron Kohonen v nghin cu v mng nron

tng quan phn trc, chng ta thy c cc c im ging v khc nhau

c bn ca: hc c gim st, mng dn tin a lp, thut ton lan truyn ngc

vn rt ph bin. Khi nghin cu v mng nron, so vi c im ca hc c

gim st, hc cnh tranh, mng nron Kohonen cu trc n gin m hiu qu

cao.

Mng nron Kohonen c s dung trong rt n hiu ng d ng, thng thng

trong vic gom cum va /hoc m hinh hoa d liu a chiu thanh cac li co hai

hoc ba chiu . C th k n l nhn dng ting ni (Kohonen, 1989, robotics

(Ritter et al ., 1989), my o (Oja, 1992), ti u t hp (Fort, 1988), phn lp

(Kohonen,1984)....


36

CHNG II

NG DNG MNG NRON KOHONEN TRONG BI TON

NHN DNG CH VIT TAY TING VIT

2.1. Tng quan v bi ton nhn dng

Bi ton nhn dng tuy ra i t thp nin 60 ca th k trc nhng n vn

lun nhn c s quan tm, nghin cu ca nhiu nh khoa hc trn th gii.

c bit l trong nhng thp k gn y, cng vi qu trnh y mnh tin hc

ha trong mi lnh vc i sng x hi, nhn dng khng ch cn l lnh vc

nghin cu l thuyt na m c ng dng rng ri trong thc t cuc sng.

Nhn dng l qu trnh phn loi cc i tng c biu din theo mt m hnh

no v gn cho chng vo mt lp da theo cc quy lut v cc mu chun.

Qu trnh nhn dng da vo cc mu hc bit trc gi l hc c gim st, hoc

khng c mu th gi l hc khng c gim st (t hc).

Cc bi ton nhn dng tiu biu c nghin cu nhiu nht hin nay bao

gm:

- Nhn dng cc mu hnh hc (vn tay, mt ngi, hnh khi,. ).

- Nhn dng ch vit (optical character recognition OCR): t mt vn bn

in hoc vit tay trn giy, nhn bit tng k t v chuyn chng thnh mt

tp vn bn trn my tnh.

- Nhn dng ting ni (speech recognition): t sng ting ni, nhn bit v

chuyn chng thnh d liu vn bn tng ng.


37

- Dch t ng (machine translation): t mt tp d liu vn bn trong mt

ngn ng (v d nh ting Anh), my tnh dch v chuyn thnh mt tp

vn bn trong mt ngn ng khc.

- Tm tt vn bn (text summarization): t mt vn bn di (gm nhiu

trang chang han), my tnh tm tt thnh mt vn bn ngn hn vi nhng

ni dung c bn.

- Tm kim thng tin (information retrieval): t mt ngun gm rt nhiu

tp vn bn hay ting ni, tm ra nhng tp c ni dung lin quan n mt

vn (mt cu hi) ta cn bit (hay cn tr li). in hnh ca cng ngh

ny l Google, mt h tm kim thng tin trn Web, m hu ht chng ta

u s dng thng xuyn. Cn ni thm rng mc d hu hiu hng u

nh vy, Google mi ch c kh nng cho chng ta tm kim cu hi di

dng cc t kha (keywords) v lun tm cho chng ta rt nhiu ti liu

khng lin quan, ngc li, c rt nhiu ti liu lin quan tn ti th

Google li tm khng ra.

- Trch chn thng tin (information extraction): t mt ngun rt nhiu tp

vn bn hay ting ni, tm ra nhng on bn trong, l mt s tp lin

quan n mt vn (cu hi) ta cn bit (hay cn tr li). Mt h trch

chn thng tin c th ln vo tng trang Web lin quan, phn tch bn

trong v trch ra cc thng tin cn thit.

- Pht hin tri thc v khai ph d liu vn bn (knowledge discovery and

text data mining): t nhng ngun rt nhiu vn bn thm ch hu nh

khng c quan h vi nhau, tm ra c nhng tri thc trc cha ai

bit. y l mt vn rt phc tp v ang giai on u ca cc

nghin cu trn th gii.


38

Ngoi ra, cn nhiu bi ton v cng ngh x l ngn ng khc, nh giao

din ngi my bng ngn ng t nhin, cc h hi p, cc h sinh ra ngn ng

... [1]. Chng c p dng vo nhiu lnh vc nh y hc, dc hc, xy dng,

qun l giao thng, d bo chy rng, t ng ha iu khin robot, iu khin

cc thit b bng ging ni, . Mt s sn phm c nghin cu v c

ng dng trn th gii v Vit Nam nh: xe y thuc thng minh ti cc bnh

vin Anh s dng cng ngh nhn dng m vch trn tay cc bnh nhn

pht thuc v theo di sc khe cho bnh nhn trnh nhng s nhm ln khng

ng c. Ti Vit Nam, cc k s ca cng ty TOSY [8] nghin cu v sng

to ra 1 con robot nh bng bn (c tn l Topio) ti International Robot

Exhibition 2007 - trin lm robot ln nht th gii khai mc ngy 29/11, ti

Tokyo. Trong c s dng cng ngh nhn dng bng di chuyn v lp

chin thut nh tr

Bn cnh s pht trin v ng dng rng ri l cc phng php nhn

dng c s dng, di y l cc phng php nhn dng c bn:

- RFID (Radio Frequency Identification) l k thut nhn dng bng sng

v tuyn t xa, l h thng khng dy cho php t ng nh n dang thu nhp d

liu k ca d liu khng tip xuc oc hoc tai liu vit tay . RFID u im l:

RFID x l t ng, tit kim nng lng v nhc im l: RFID c gi

thnh cao nn khng th ng dng rng ri, cha c chun chung, cha c cc

gii php hiu qu ).

- SVM (Support Vector Machines) l mt phng php my hc tin tin

c nhiu thnh cng khng ch trong cc lnh vc khai ph d liu m cn

trong lnh vc nhn dng. Trong nhng thp nin gn y, SVM c nh


39

gi l mt trong nhng phng php phn lp c chnh xc rt cao v cng

c p dng nhiu trong cc bi ton nhn dng ch vit tay.

- Dynamic programming: l phng php dng gii quyt cc bi ton

ti u, bt u t vic gii quyt cc bi ton nh nht n bi ton hon

chnh.Tn dng kt qu tnh ton trc trnh lp li vic hon tt.

Dynamic programming c nhng u im: khng phi tnh li cc bi ton con

nu trc tnh ri, tc tnh ton nhanh hn cc phng php thng

thng, phc tp tnh ton thng l cc a thc. V c nhng nhc im:

Khng phi bi ton ti u no cng dng c phng php ny, khng c

phng php tng qut, thng phc tp v mang nhiu tnh th thut.

- HMM (Hiden Markov Model): u im l thit k v coding n gin,

khng dng nhiu b nh. Nhc im l rt kh phn lp d liu.

2.2. Gii thiu v bi ton nhn dng ch vit tay Ting Vit

Nhn dng ch ci Ting Vit cng nh nhn dng ni chung l dng cc

thut ton tm ra cc c im ring ca tng c th trong qun th m chng

ta phi nhn dng. Vi mi d liu nhp vo ta s phi xut ra mt kt qu tng

t nht. Nhn dng ch ci Ting Vit bao gm hai kiu chnh l nhn dng

ch in v nhn dng ch vit tay.

Trong khi nhn dng ch in c xem l vn c gii quyt t ti

chnh xc rt cao vi s ra i ca nhiu h thng nh: H nhn dng ch in

da trn m hnh mng Nron bn lp ca hai tc gi J.Wang v J.S.N. Jean c

t l nhn dng chnh xc t ti 99.75%. Phn mm Simple OCR l mt phn

mm kh mnh dng cho my qut c hng trm ngn ngi s dng trn

th gii. L mt cng c mnh v nhn dng k t quang hc thay cho vic nh

my nhm chn, ngoi ra phn mm ny cn c th nhn dng ch vit tay v


40

hc t mi. Vit Nam cng c sn phm VnDOCR ca Vin Cng ngh

thng tin chng trnh h tr nhn dng cho cc dng nh PDF, TIFF, JPEG,

GIF, PNG, v BMP. Qua rt nhiu th nghim cho thy VnDOCR nhn

dng ch in ting Vit rt thnh cng vi chnh xc rt cao.

Tuy nhin, cho n ngy nay th nhn dng ch vit tay c th ni l cha

c ng dng nhiu trong thc t, nhn dng ch vit tay c thc hin qua

hai hnh thc chnh l nhn dng ch vit tay trc tuyn (online) v nhn

dng ch vit tay ngoi tuyn (offline). C th bi ton nhn dng ch trc tuyn

(online) l nhn dng cc ch trn mn hnh ngay khi ch c vit. Trong h

nhn dng ny my tnh s lu li cc thng tin v nt ch, th t nt vit, hng

v tc ca nty chnh l c s my tnh nhn din c ch ci, do

vic nhn dng khng gp qu nhiu kh khn. H thng nhn dng ch vit

tay hn ch trc tuyn trn mt trm lm vic ca IBM do nhm nghin cu

gm H.S.M.Beigi, C.C.Tapert, M.Ukeison v C.G.Wolf phng thc hnh

Watson IBM ci t l mt trong nhng sn phm nhn dng ch vit tay online

tiu biu nht. Nhn dng ch trc tuyn (online) c ng dng trn cc my

nh: Tablet PC, Palmtop, PocketPC, .V cc thit b trn c s h tr cc thao

tc vi bt v mc, cho php ngi dng c th giao tip bng cch dng bt v

trc tip ln mn hnh. Vi nhn dng ch vit tay ngoi tuyn (offline) th d

liu u vo c cho di dng cc nh. Kt qu ca nhn dng ch vit tay

offline hin nay cn rt nhiu nhc im v gp rt nhiu kh khn nh:

- Vi ch vit tay c mt kch thc ging nhau tht l kh, chng ta

khng th m bo c ch vit ca cng mt t trn mt dng hay cng mt

k t trong mt vn bn do mt ngi vit c th c kch thc nh nhau.


41

- Mi mt ngi c mt kiu v dng ch khc nhau. C ngi th vit ch

thng hay nghing v bn phi, hay nghing v bn tri v cng c ngi

nghing nhiu

- Khng ch kiu ch, kch thc, hnh dng khc nhau m ch vit tay i

khi cn b thiu nt tha nt, gia cc k t trong cng mt t thng c nhng

nt ni hoc thm ch chng cn b dnh vo nhau hay k t thuc dng di b

dnh, b chng ln cc k t thuc dng trn nn rt kh khn trong vic tch

dng, xc nh phn cch gia chng.

Tuy nhn dng ch vit tay gp rt nhiu nhng kh khn nhng nhn dng

ch vit tay cng c mt s chng trnh tiu biu c th k n nh: H thng

phn loi t ng a ch th bu in ca tc gi M.Pfister, S.Behnke v

R.Rojas i hc tng hp Berlin, c. H nhn dng ch vit tay trong lnh

vc kim tra ti khon ngn hng ca nhm nghin cu Simon v O.Baret

Paris. Vit Nam, chng ta mi ch c c nhng sn phm th nghim nh h

thng nhn dng ch s v ch ci vit tay ri rc trn cc phiu xut nhp cnh

ca nhm nghin cu i hc quc gia thnh ph H Ch Minh, C th ni,

bi ton nhn dng ch vit tay vn cn c u t nhiu thi gian v cng sc

ca con ngi c c nhng sn phm c ngha thc tin rng hn.

Hin nay c rt nhiu phng php nhn dng, v di y lit k vi

phng php nhn dng c bn:

- Dng mng Nron: u im l thit k v coding n gin, nhc im l

tnh chm v xc sut khng cao.

- Dng HMM (Hiden Markov Model): u im l thit k v coding n gin,

khng dng nhiu b nh. Nhc im l rt kh phn lp d liu.


42

- Dynamic programming: n gin, nhng hiu qu khng cao.

D l phng php no th vic nhn dng ch vit u thng c tin

hnh theo m hnh cc bc nh sau:

Hnh 2.1: M hnh chung trong nhn dng ch vit

Trong :

Tin x l: : l qu trnh chun ha d liu vo, gm cc cng vic nh

x l nhiu, chun ha kch thc d liu, ...

Trch chn c trng: l qu trnh tm ra cc thng tin hu ch v c

trng nht cho mu u vo s dng cho qu trnh nhn dng.

Nhn dng: l qu trnh s dng mt m hnh nhn dng c th vi mt

thut ton c th tr li mu u vo l ch (k t) no.

Hu x l: l qu trnh x l kt qu cho ph hp vi tng ng dng c

th.


43

Nh vy, chng ta c bit s qua tnh hnh chung ca bi ton nhn

dng ch vit trn th gii cng nh Vit Nam: nhng ng dng thc t,

nhng kt qu t c v nhng g chng ta cn phi c gng thm na c

bit l vi bi ton nhn dng ch vit.

2.3. Phng php nhn dng ch vit tay s dng mng nron

i vi ch vit tay ca con ngi, cng vic nhn dng kh phc tp do tnh

qu a dng, khng ng nht, c tnh t nhin ca con ngi.

Mt s phng thc lp trnh truyn thng nh x nh k t vo trong

ma trn, phn tch nh hoc vct d liu, kim tra a ra quyt nh ph hp

ca kt qu. Trong lp trnh truyn thng, vic thc thi ny cn vit m ngun v

tn cho mi kiu u vo khc nhau. L thuyt ny khng hin thc.

Phng sinh hc v c bit l phng nron thn kinh l mong c t lu ca

nhn loi. Chnh nhng khm ph ca khoa hc v b no con ngi, v nron

thn kinh thc y cc nh tin hc nghin cu xy dng nhng h thng m

phng hot ng ca b no con ngi. Mc d c nghin cu cch y kh

lu nhng nhng nm gn y vic nghin cu nron v mng nron mi c

nhng thnh cng nht nh. Phng php nhn dng dng mng nron mang

nhiu trin vng v ha hn s gii quyt c nhng vn m cc phng

php truyn thng cn mc phi, cho php cc chng trnh nhn dng tin gn

n kh nng nhn dng ca con ngi thng qua c ch hc.

S dng mng nron nhn to vi nhng bc lm vic ng quy tc, t

vic cp nht li cc trng s lin kt gia cc nt mng. Mng c u im l c

th nhn d liu t nhng phn tch sinh ng ca cc nh u vo v vic hun

luyn cho cc k t u ra cho mu. Ni cch khc l mng c kh nng thch

nghi vi mi trng d liu u vo sinh ng.


44

2.4. Pht biu bi ton

Cho bi ton nhn dng k t vit tay ting Vit ri rc trc tuyn. Yu cu

xy dng chng trnh nhn dng vi u vo l giao din cho php ngi s

dng v k t ln, c u ra l k t tng ng vi k t v vo. Chng

trnh s dng cng c l mng nron, c th trong lun vn ny dng mng

nron Kohonen.

tng bi ton :

To giao din v k t.

Chuyn i nh k t sang ma trn im nh.

Chuyn thnh vct tuyn tnh v a vo mng nron.

Da vo mng nron hun luyn mng vi tp k t cn nhn dng.

V k t cn nhn dng.

Chuyn i nh k t sang ma trn im nh.

Chuyn thnh ma trn tuyn tnh v a vo mng nron.

Tm ra k t trong ng vi k t v.

2.5 Cc bc gii quyt bi ton s dng mng nron Kohonen

Xy dng giao din v.

Xy dng mng nron Kohonen.

X l d liu (phn tch nh).

Hun luyn mng nron Kohonen.

Nhn dng mng nron Kohonen.

2.5.1.Xy dng giao din v

- Xy dng mt giao din ha, cho php ngi s dng dng chut v

k t cn nhn dng.


45

- Tm gii hn trn, di, tri, phi ca k t sau khi c v.

- Ct b tt c cc khong trng xung quanh k t c v, thu c nh

ch c hon ton k t. Nh th bi ton quy v x l nh ch c mi k t

m khng quan tm k t c v v tr no.

Hnh 2.2: Qu trnh tm gii hn k t

- Thc hin ly mu xung nh ca k t bng cch nh x k t vo mt

li c kch thc 10* 10. Bng cch ny ta quy k t v mt kch thc

c nh, nh vy khng cn quan tm n kch thc k t c v vo l

to hay nh.

Hnh 2.3: Qu trnh ly mu xung


46


47

2.5.2. Xy dng mng nron Kohonen

Mt vic rt quan trng y l vic quyt nh c ca mng. Vic nh

c u vo ph thuc vo vic nh c li ly mu xung, Nu ta chia nh k

t thnh ma trn c kch thc ln th k t s c biu din mt cch chi tit.

Tuy nhin, vic ny dn n chi ph x l cc ma trn rt ln. Ngc li, nu ta

dng ma trn kch thc nh biu din nh k t s dn n vic mt mt

thng tin. cho cn bng v hp l, ta s chun ha c ca ma trn bng

10*10, tc l nh s c biu din bi 100 phn t.

Lp u vo gm 100 noron nhn gi tr t 100 thnh phn tng ng ca

vct u vo. D liu u vo ny c c t vic vct ha t ma trn im

nh k t bng phng php chia li.

Lp u ra c s nron bng vi s mu nhp vo.

2.5.3. X l d liu (phn tch nh)

Qu trnh phn tch nh l qu trnh tm ra c tnh ca k t. Cc im nh

ny chnh l gi tr u vo cho c qu trnh hun luyn v qu trnh kim tra.

Qu trnh phn tch ny da trn vic nhn dng t nh ngi s dng v vo

bng phng php tm cc im en RGB(0,0,0) hoc im trng

RGB(255,255,255). Kt qu thu c l ma trn im nh. Sau ma trn ny

s c nh x thnh vct u vo c kch thc 100 phn t. Trc khi a

vo mng vct ny cn c x l lm ni im nh thnh vct gm cc phn

t 0.5 v -0.5.


48

Hnh 2.4 Qu trnh nh x t ma trn im sang ma trn gi tr

2.5.4. Hun luyn mng nron Kohonen

Mt mng nron c xy dng s phi c hun luyn trn mt khng

gian u vo c chun b trc. Khi hot ng, mng nron s c gi tr

c hun luyn.

S phc tp ca cc tham s cho vic hun luyn mng: Vic chn gi tr

cho cc tham s (tc hc, s ln lp cn thit, gi tr ngng ca li ... ) c

da vo kinh nghim v qua nhng ln tin hnh thc nghim.

Mc ch ca qu trnh hun luyn l hiu chnh trng s W sao cho ging

vi vct u vo nht. Thc hin hiu chnh cc vct trng s ng vi tng k

t mu. Kt qu thu c mt ma trn trng s W ging vi tp vct u vo.

Hun luyn bao gm cc bc:

Thit lp cc tham s u vo.

Tt c cc mu u vo c ly mu hnh nh k t xung li kch

thc 10*10. Ta c mt ma trn hai chiu kch thc 10*10 c cc

gi tr tng ng vi gi tr cc im nh.

Chuyn thnh cc vct u vo c kch thc 10* 10.

a cc vct u vo vo mng.

Thc hin tm ma trn trng s tt nht theo s thut ton


49

Hnh 2.5 Qu trnh hun luyn mng nron Kohonen


50

2.5.5 Nhn dng mng nron Kohonen

Qu trnh nhn dng c din ra theo cc bc sau:

Bc 1: Ngi s dng v k t cn nhn dng.

Bc 2: K t c ly mu xung li kch thc 10*10. Ta c mt ma

trn hai chiu kch thc 10* 10 c cc gi tr tng ng vi gi tr cc im

nh.

Bc 3: Chuyn ma trn im nh thnh vct u vo c kch thc 10* 10

bao gm cc gi tr 0.5, - 0.5.

Bc 4: Vct u vo c a vo mng nron tm nron chin thng.

Bc 5: Thit lp mng cha cc k t trong tp mu, vi ch s ca mng

tng ng vi ch s ca nron u ra.

Bc 6: nh x nron chin thng vo mng trn tm ra k t tng ng

vi nron chin thng.

Bc 7: Hin th kt qu nhn dng c tng ng vi k t c v.

2.5.6 Kt lun

C nhiu phng php gii quyt bi ton nhn dng k t vit tay

ting Vit. Nu p dng mng nron gii quyt, thng thng ngi ta hay s

dng mng dn tin a lp cho vic thc hin nhn dng. Nhng chng ta s

thy mt s kh khn trong vn tm ra s nron trong tng lp, nht l lp n.

Thut ton lan truyn ngc cng phc tp hn, nhiu cng thc tnh ton hn,

li phi xt trn tng lp mng. Trong khi , mng nron Kohonen cng l mt

loi mng rt ph bin, c cu trc n gin hn, cc bc thc hin n gin,


51

r rng, d dng la chn v hiu chnh cc tham s u vo, qu trnh hun

luyn mng nhanh, d hi t.

V vy, la chn mng nron Kohonen gii quyt bi ton nhn dng k

t vit tay ting Vit ri rc trc tuyn s n gin v hiu qu hn.


52

CHNG III

M PHNG NHN DNG K T VlT TAY TING VIT

RI RC S DNG MNG NRON KOHONEN

3.1 Gii thiu

Trong lun vn ny do hn ch v mt thi gian v phc tp ca bi ton

nhn dng ch vit tay ting Vit cho nn ti ch hn ch m phng nhn dng

k t vit tay ting Vit ri rc trc tuyn. Cc k t ting Vit gm k t khng

du {A, B, C, D, , E, G, H, I, K, L, M, N, O, P, Q, R, S, T, U, V, X, Y} v k

t c du {, , , , , , , , , , , , , , , , , , , , , , ,

, , , , , , , , , , , , , , , , , , , , , , , , , , , ,

, , , , , , , , , , , , , , }.

Chng trnh ny c hun luyn c th nhn dng k t vit tay do

ngi s dng v chng, chc nng ny tng t nh nhn dng k t vit s

dng cc thit b cm tay PDA (Personal Digital Assistant ). Chng trnh gm

mt giao din n gin cho php ngi s dng dng chut v k t cn nhn

dng v tin hnh nhn dng.

Khi v k t c mt hnh ch nht xung quanh k t . Mc ch ca hnh

ch nht ny l ct bt k khong trng no khng lin quan n k t, lm

cho chng trnh c kh nng khng cn quan tm n v tr ca k t c vit.

Ta c th v k t gia, trn, di hay bt k mt v tr khc nhng chng

trnh vn c kh nng nhn dng ng.

Sau khi v k t, k t c ct b khong trng xung quanh m khng lin

quan n k t, sau c ly mu xung v k t c v c phn gii qu


53

cao m mng nron khng hiu c. Gim mu hnh nh, hnh nh c nh x

vo mt li nh c kch thc 10*10. Nhn vo y ta c th thy c hnh

nh ca k t. Nh ly mu xung nn s u vo t hn khi k t y kch

thc. ng thi k t c quy v kch thc c nh, do khng cn phi

quan tm k t c v ln hay nh khi hun luyn hay khi nhn dng.

Mu c a n mng nron Kohonen v nron chin thng c la

chn. Chng trnh tr v k t tng ng vi k t ngi s dng v. S nron

u ra bng s k t nhn dng cha trong tp mu.[9]

3.2 Thc hin chng trnh nhn dng k t

S dng ngn ng java m phng cho vic s dng mng nron Kohonen

nhn dng k t vit tay ting Vit ri rc trc tuyn.

Mt s lp c s dng cho chng trnh ny:

Entry.java: Khu vc v k t cho php ngi s dng v k t cn nhn

dng.

KohonenNetwork.java: Mng nron Kohonen. Thc hin cc phng

thc l duy nht i vi mng nron Kohonen. y l ni mng nron Kohonen

c hun luyn.

MainEntry.java: Khung chnh ca ng dng, lp ny bt u ng dng

nhn dng k t vit tay.

Network.java: Cc hm chung cho mng nron, khng ch ring cho

mng Kohonen. Lp ny tnh chiu di vct, tch v hng v cc cng vic

chung khc ...


54

Sample.java: c s dng hin th hnh nh c ly mu xung trn

li kch thc 10* 10.

SampleData.java: c s dng lu gi cc tham s ca hnh nh ly

mu xung.

TrainingSet.java: Gm cc vct u vo kch thc 100 phn t

hun luyn cho mng nron.

3.2.1 Xc nh cc tham s cho mng

C rt nhiu loi mng nron khc nhau. Hu ht c t theo tn ngi

sng to ra n. Mng nron s c s dng trong ng dng ny l mng nron

Kohonen. Cc k t sau khi v, c ly mu xung v c a vo u mng

nron. C mt nron u vo cho mi im nh trong hnh nh c ly mu

xung. V hnh nh c ly mu xung c kch thc 10*10 nn c 100 nron

u vo. S nron u ra bng s k t mu.

Ngoi yu t u vo v u ra cn c cc kt ni gia cc nron. Cc trng

s ny khng bng nhau i vi tt c cc kt ni. Mi kt ni c ch nh mt

trng s. Trng s ny l yu t duy nht xc nh u ra mng nron ng vi

mi mu u vo. xc nh tng s kt ni phi nhn s nron u vo vi s

nron u ra. Mng c kt ni y ngha l mi u vo c kt ni vi tt

c cc u ra. Qu trnh o to l qu trnh tm ra cc gi tr chnh xc cho cc

trng s ny.


55

3.2.2 V hnh nh

Mc d khng trc tip lin quan n mng nron, song qu trnh ngi s

dng v k t l mt phn quan trng ca ng dng nhn dng k t vit tay

ting Vit.

Lp ny nh ngha mt s thuc tnh c m t nh sau:

downSampleTop: Cnh trn ca vng ct c s dng khi ly mu

xung.

downSampleBottom: Cnh di ca vng ct c s dng khi ly mu

xung.

downSampleLeft: Cnh tri ca vng ct c s dng khi ly mu

xung.

downSampleRight: Cnh phi ca vng ct c s dng khi ly mu

xung.

entryGraphics: Mt i tng ha cho php v hnh nh ln vng

v tng ng vi vng v k t.

entryImage: Nhng hnh nh k t m ngi s dng v.

lastX: Ta x cui cng m ngi s dng v ti .

lastY: Ta y cui cng m ngi s dng v ti .

pixelMap: S lng pixel m ly mu xung, iu ny c thc hin t

entryImage.

ratioX: T l ly mu xung theo chiu x.


56

ratioY: T l ly mu xung theo chiu y.

sample: i tng s cha hnh nh c ly mu xung.

Hu ht cc k t v c x l bi processMouseMotionEvent. Nu ngi

s dng r chut v th c mt ng c ni t v tr t chut u tin n

v tr hin ti ca chut. ng ny c v ra mn hnh trong khung v k t

tng ng vi k t v vo.

3.2.3 Ly mu xung hnh nh

Mi ln k t c v hun luyn hay nhn dng, n phi c ly mu

xung.

3.2.3.1 Lu hnh nh c ly mu xung

Hnh nh c ly mu xung c lu trong lp SampleData. Chng trnh

thc hin vi mt li kch thc 10*10. Tt c hnh nh c ly mu xung

c lu trong lp ny. Lp SampleData cng bao gm cc phng thc thit

lp v nhn c d liu lin kt vi li ly mu xung. Lp SampleData cng

cha mt phng thc, t tn l clone, s to ra mt bn sao chnh xc ca hnh

nh ny.

3.2.3.2 Kch thc v v tr

Tt c hnh nh c ly mu xung trc khi c s dng. iu ny gip

cho mng nron khng b nhm ln v v tr v kch thc. Vng v ln

c th v k t vi cc kch thc khc nhau. Bng cch ly mu hnh nh xung

mt kch thc ph hp, do khng cn quan tm n vn k t c vit

c kch thc nh th no.


57

Khi v mt k t, u tin chng trnh s v mt hp xung quanh bin

ca k t. iu ny cho php loi b tt c khong trng xung quanh k t c

v. Qu trnh ny c thc hin bn trong phng thc downsample ca lp

Entry.java. Thc hin ct hnh nh ny, v cui cng ly mu xung, chng ta

phi ly cc mu bit ca hnh nh k t. iu ny c thc hin bng cch s

dng mt lp "PixelGrabber".

ct hnh nh v loi b bt k khong trng xung quanh, vic ct c

thc hin bng cch ko bn ng o t trn, bn tri, bn phi va t di ca

hnh nh, nu gp im nh no th dng li khng qut na. Bng cch ny bn

ng thng s l cc cnh ngoi ca hnh nh. C hai phng thc hLineClear

v vLineClear chp nhn mt tham s cho bit dng qut, v tr v gi tr true

nu dng l trng. Chng trnh hot ng bng cch gi hLineCIear v

vLineClear cho n khi gp cnh ngoi ca k t. tnh ton ng bin trn

cng ca hnh ch nht gii hn k t, chng trnh bt u t 0 v tip tc

xung di hnh nh. tm ng bin di thc hin qut ngc li t di

y hnh nh k t ln. Cc quy trnh xc nh gii hn tri v phi c thc

hin cng theo cch ny.

3.2.3.3 Thc hin ly mu xung

Sau khi k t c ct n s c ly mu xung. Hnh nh c phn gii

ln c gim xung thnh phn gii 10*10. Tng tng rng ta v mt

li ln trn k t, phn chia thnh cc hnh vung vi 10 ng ngang va 10

ng xung, Nu bt k im nh no c in y th trong li 10* 10

im nh tng ng cng c in y. Phn ln cng vic thc hin qu trnh

ny c thc hin trong phng thc "DownSampleQuadrant".


58

Phng thc "downSampleRegion" chp nhn s lng vng cn c tnh

ton. u tin, phi tnh ton ta x, y ban u v cui cng . Phng thc

"downSampleLeft" c s dng tnh ton ta x cho vng u tin, y l

cnh bn tri ca hnh ch nht bao quanh k t. Sau x c nhn vi h s

t l x. l t l bao nhiu pixel cho mi vung. iu ny cho php xc nh

ni t "startX", v im bt u "startY" c tnh ton theo cch tng t.

Tip theo lp vi mi ta x v y thuc mi hnh vung, Nu c s chn pixel

th in y, sau phng thc tr li gi tr ng. iu ny ch ra rng min

ny c in y.

3.2.4 Cc tp hun luyn

hun luyn mng phi cung cp cc tp hun luyn. D liu hun luyn

ny c lu trong cc lp TrainingSet.

Trong cc lp Trainingset lu cc bin sau:

inputCount: S cc yu t u vo cho mi mu o to.

outputCount: S cc yu t u ra cho mi mu o to.

input[] []: Mu u vo hun luyn.

output[][]: Mu u ra hun luyn.

trainingSetCount: S lng mu hun luyn

3.2.5 Lp mng c bn

Cc thuc tnh c s dng cho cc mc ch sau:

NEURON_ON: Gi tr m mt nron phi ln hn hoc bng c coi

l "on".


59

NEURON_OFF: Gi tr m mt nron phi nh hn hoc bng c

coi l "off".

output[]: u ra ca mng nron.

totalError: Li t lt cui cng. y l tng 1i ca tt c tp hun

luyn.

inputNeuronCount: s nron u vo.

outputNeuronCount: s nron u ra.

random: B to s ngu nhin, c s dng khi to trng s c gi

tr ngu nhin.

Lp mng bao gm phng thc tnh chiu di vct cho mt vct. Phng

php ny tnh tng bnh phng cc s c trong vct. Mt chc nng quan

trng khc ca cc lp c s l tnh tch v hng. Lp mng Kohonen c

cung cp nh mng con.

Trng s c khi to ban u vi cc gi tr ngu nhin. Cc gi tr ngu

nhin ny c hun luyn to ra kt qu tt hn. Lc bt u ca mi chu k

hun luyn cc trng s cng c khi to ngu nhin. Lp mng to ra mt

phng thc lm iu ny.

3.2.6 Lp mng nron Kohonen

Cc thuc tnh c s dng bi mng Kohonen c tm tt nh sau:

Halt: thit lp bng true kt thc hun luyn.

learnMethod: phng thc hc, thit lp bng 1 cho tr, hoc gi tr khc

cho cng.


60

learnRate: tc hc ban u.

outputWeights[][]: trng s nron u ra v u vo.

quitError: Khi t n t l 1i ny th ngng hun luyn.

reduction: Lng gim learnRate mi chu k

retries: Tng s chu k cho php, s chu k hun luyn cao nht c th

din ra.

train: Tp hun luyn

u tin, cn lu rng c mt phng thc dng sao chp ma trn trng

s. Sao chp ma trn trng s l iu quan trng bi v khi hun luyn mng

Kohonen, ma trn trng s mi tm c tha mn l ma trn trng s tt nht,

n phi c sao chp lu li ma trn trng s tt nht ny. Cng c mt

phng thc c kh nng xa trng hon ton ma trn trng s. N thc hin

bng cch thit lp tt c cc trng s ca ma trn bng 0. Cui cng c mt

phng thc khi to s thit lp tt c ma trn trng s gi tr khi to ngu

nhin.

Mt s phng thc khc nhau c s dng chun ha, bi v chun ha

l mt phn quan trng ca mng Kohonen. Chun ha cho mng Kohonen

hot ng tt: Chun ha u vo, chun ha trng s.

Khi hun luyn, chng ta khng quan tm n u ra ca mi nron m ch

quan tm n u ra ca nron thc s chin thng. Phng thc "winer" tm

nron chin thng hot ng bng cch lp trn tng nron v tnh ton u ra

ca tng nron ring bit. Trong vng lp ny s lu li ch s ca nron c u


61

ra cao nht. Nron vi u ra cao nht c coi l nron chin thng. Phng

thc tr li nron chin thng.

3.2.6.1 Tnh ton u ra ca mng Kohonen

Qu trnh nhn dng bt u khi m ngi s dng v k t v nhn vo nt

nhn dng. u tin k t c ly mu xung thnh hnh nh kch thc 10*10.

Hnh nh c ly mu xung phi c sao t mng hai chiu n vct u

vo m s dng a vo mng. Mng nron yu cu lm ni im u vo. V

vy gn gi tr 0.5 v -0.5 cho cc im nh.

Mt mng 100 gi tr c a vo u vo. iu ny c thc hin bng

cch gi cc mng u vo n phng thc "winner" ca mng Kohonen. N

s tr li nron chin thng ca 100 u vo c lu trong s nguyn "best".

Nron chin thng khng phi l qu hu ch, bi v n khng cho bn thy

nhng k t thc s c nhn dng. sp xp cc nron vi cc k t

nhn dng c, mi hnh nh k t m mng c o to phi c a

vo mng v nron chin thng c xc nh. V d, mun a hnh nh hun

luyn cho k t vo trong mng, v nron chin thng l nron #4, th phi

bit rng nron #4 l nron c hc nhn dng ra mu ca k t . iu

ny c thc hin bng cch gi phng thc "mapNeurons". Phng thc

"mapNeurons" tr li mt mng k t. Ch s ca mi phn t mng tng ng

vi nron nhn dng k t .

Phn ln cng vic thc t c thc hin bng mng nron c thc hin

bng phng thc winner. u tin phng thc ny thc hin chun ha u

vo, tnh gi tr u ra cho mi nron. Nron no c gi tr ln nht th c


62

chn l nron chin thng. u tin bin "biggest" c thit lp gi tr nh

ch rng cha c nron chin thng.

Trng s ca mi nron u ra c tnh bng cch ly tch v hng ca

trng s mi nron u ra n nron u vo. Tch v hng c tnh bng

cch nhn mi gi tr u vo vi trng s gia nron u vo v u ra. Nhng

trng s ny c quyt nh trong qu trnh hun luyn. u ra c gi v nu

cho n gi n l gi tr ln nht th n c thit lp l nron chin thng.

Ta thy tnh kt qu t mng nron l mt qu trnh rt nhanh. Trn thc t,

xc nh trng s ca nron l phn phc tp nht ca qu trnh ny.

3.2.6.2 Hun luyn mng nron Kohonen

Hc l qu trnh la chn mt ma trn trng s nron s nhn ra ng mu

u vo. Mt mng Kohonen hc bng cch lin tc nh gi v ti u ha mt

ma trn trng s. lm c iu ny, mt ma trn trng s khi to phi c

quyt nh. N c chn bng cc gi tr ngu nhin.

Khi ma trn trng s c khi to ngu nhin th qu trnh hun luyn c

th bt u. u tin, nh gi ma trn trng s xc nh mc li hin hnh.

Li ny c xc nh bi qu trnh nh x u vo hun luyn n u ra tt

nh th no. Li c tnh ton bng phng thc "evaluateErrors" ca lp

KohonenNetwork. Nu mc li nh, nh hn 10%, th qu trnh c hon

thnh.

Qu trnh hun luyn bt u khi ngi s dng nhn vo nt: "Hc". Qu

trnh ny tnh s nron u vo v u ra. u tin s nron u vo c quyt


63

nh t kch thc ca hnh nh ly mu xung l 100. Cn s u ra tng ng

vi s k t mu.

By gi kch thc ca mng nron c xc nh, tp hun luyn v mng

nron phi c cu trc. Tp hun luyn c cu trc gi s lng chnh

xc s mu. Vi chng trnh ny l 89 k t c cung cp.

Tip theo, hnh nh u vo c ly mu xung v c sao chp n tp

hun luyn. y l vng lp cho tt c mu u vo.

Cui cng mng c cu trc v tp hun luyn c a vo. Vi tp

hun luyn c giao, phng thc "learn" c th c gi. N s iu chnh ma

trn trng s cho n khi mng c hun luyn.

Phng thc hc s lp vi s vng lp khng xc nh. Nhng chc chn

rng n s mt nhiu hn mt ln lp. Khi s mu hun luyn ph hp vi nron

u ra, hun luyn xy ra rt nhanh.

Mt th tc c tn l "evaluateErrors" c gi nh gi cc trng s

ang lm vic tt nh th no. iu ny c xc nh bng cch nhn vo d

liu hun luyn n nron u ra tt nh th no. Nu c nhiu nron u ra

c kch hot cho cng mt mu hun luyn th tp trng s l khng tt. Mt

t l li c tnh ton da trn tp hun luyn truyn n nron u ra tt nh

th no.

Mt khi li c xc nh, chng ta phi xem n c di mc li tt nht t

trc n gi khng. Nu n tha mn th li ny c a vo mc li tt nht

v cc trng s nron c duy tr bng cch sao chp lu li.


64

Tng s nron chin thng sau c tnh ton. iu ny cho php ta xc

nh trng hp khng c nron u ra no c kch hot. Ngoi ra, nu t l

li di mc chp nhn c (10%) th qu trnh hun luyn dng. Nu khng

c nron no chin thng th mt nron buc phi tr thnh nron chin thng.

By gi ma trn trng s u tin c nh gi, n c iu chnh da

trn li ca n. Cc gi tr iu chnh c tnh ton khi li c xc nh. Qu

trnh hiu chnh ma trn trng s gm hai bc l tnh ton l

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