Matlab Io Screen

8/3/2019 Matlab Io Screen

1/20

ICT Onderzoek LUDIT

IO_sreen_1

IO_screen

MATLAB Screen IO

MATLAB offers a number of ways for entering data, both on the screen or on file.

Most of the syntax specifications are copied from the MATLAB help documentation.

Input from screen

The input function

MATLAB can prompt you for input at any time by using the input command. This

command will display a text string, if specified, and waits for input.Table IO_screen-1. input function

Function Description

input Prompts user for input

user_entry = input('prompt')

displays prompt as a prompt on the screen,

waits for input from the keyboard, and

returns the value entered in user_entry.

Entering any letter will create an error.

user_entry = input('prompt','s')

returns the entered string as a text variable

rather than as a variable name or numerical

value. This form will either take numbers

or strings as entry; the user_entry variable

will always be a string, even if a number is


2/20

ICT Onderzoek LUDIT

IO_sreen_2


entered.

The response to the input prompt can be any MATLAB expression, which is evaluated

using the variables in the current workspace: if you enter a series of numerical values

between [ ], these values will be considered as a array (this is a way to enter multiple

data). This command is quick and useful for taking in a single line of keyboard entry.

Single value input

An example of the use of input using numerical data is given in demo_input_01.m

%% use of the input function for an interactive approach%ht = input('Enter the height of the cylinders (m)? ');mx_diam = input('Enter the maximum diameter (m)? ');

Running the script produces this result

>> demo_input_01

Enter the height of the cylinders (m)? 5

Enter the maximum diameter (m)? 6

When the 's' option is specified in the input command (input(prompt,s)), theentered string is returned as-is, as shown in demo_input_02.m. Matlab provides a set of

string conversion functions that can be applied to extract the right data out of the string.


>> demo_input_02

Enter your data: this is a string

Name Size Bytes Class Attributes

inp_data 1x16 32 char

inp_data =

this is a string

Multiple value input

An example of the use of input where multiple values can be entered is given in

demo_input_03.m

%vec = input('Enter a set of numerical values (Enter the values between [ ])');


3/20

ICT Onderzoek LUDIT

IO_sreen_3


>> >> demo_input_03

Enter a set of numerical values (Enter the values between [ ])[1 2 3]

mean of the values entered:

mean_calc =

2

TIP: Be sure to tell the user how to enter the data, especially if it is to

be entered according to a specific format

Input dialog boxes

Besides the standard input command, MATLAB also provides a few dialog boxes that

can be used to enter data interactively. These graphical elements are easy to include in

(existing) MATLAB code; this approach is different from the MATLAB GUI way!

MATLAB is very well suited for providing a proof of concept. If you want to

demonstrate quickly that a concept is fundamentally correct, you code it and debug it

quickly in MATLAB. Most of the times these programs have some tunable parameters

which need to be adjusted by the user. It is of no good practice to let the user dig into

your code to change a parameter, but it is preferable that these values are entered using a

dialog box. MATLAB's own ready-to-go dialog boxes are almost always sufficient forthis.

Table IO_screen-2. Input dialog boxes


inputdlg Create input dialog box

answer = inputdlg(prompt,dlg_title,num_lines,defA

and returns user input for multiple prompts in the cell array.

prompt is a cell array containing prompt strings.

dlg_title specifies a title for the dialog box.num_lines specifies the number of lines for each user-entered

value. num_lines can be a scalar, column vector, or matrix.

defAns specifies the default value to display for each prompt.

defAns must contain the same number of elements as prompt

and all elements must be strings.

listdlg Create a list dialog box that enables the user to select one or

more items from a list.


4/20

ICT Onderzoek LUDIT

IO_sreen_4


[Selection,ok] = listdlg('ListString',S)

Selection is a vector of indices of the selected strings (in single

selection mode, its length is 1). Selection is [ ] when ok is 0. ok

is 1 if you click the OK button, or 0 if you click the Cancel

button or close the dialog box.

Double-clicking on an item or pressing Return when multiple

items are selected has the same effect as clicking the OK

button.

menu Generate menu of choices for user input

k = menu('mtitle','opt1','opt2',...,'optn')

the menu is displayed with a title is in the string variable

'mtitle' and the choices are string variables 'opt1', 'opt2', and so

on.

menu returns thenumber of the selected menu item

The inputdlg function

This command is useful for taking in multiple lines from the keyboard all at once.

The code for the inputdlg consists of two parts. The first creates the box with appropriateentry labels and title, and the second where the entries are converted to a form that is

usable by Matlab. The four arguments (prompt, dlg_title, num_lines, and defAns) are

variables; they must be defined in advance. The entries initially are returnded as a cell

array and must be converted before they can be used in calculations. This is done using

curly brackets {} to access the cell contents.

Numerical data, characters, and file names can all be entered in a dialog box. Inside a

dialog box you can move from field to field either with the mouse or by using the tab

key.

An example of the use of inputdlg is given in demo_inputdlg_01.m

% define the labels for the individual entries (between curly braces {})

prompt = { 'Temperature (K)', 'Pressure (Pa)', 'Filename'};

% define a title for the dialog boxdlg_title = 'Data Entry for Problem 1';

% create the dialog box with the inputdlg commandanswer = inputdlg(prompt, dlg_title);

Running the program produces this result


5/20

ICT Onderzoek LUDIT

IO_sreen_5

Figure IO_screen-1. dialog box demo_inputdlg_01

A more complex example, with predefined default values is given in

demo_inputdlg_02.m

% define the labels for the individual entries (between curly braces {})prompt = { 'Entry 1', 'Entry 2', 'Entry 3'};

% define a title for the dialog boxdlg_title = 'Data Entry for Problem 2';

% define default answersdefAns = {'[1 2 3]', 'water', 'A'};

% create the dialog box with the inputdlg commandanswer = inputdlg(prompt, dlg_title, [3;2;1], defAns);



6/20

ICT Onderzoek LUDIT

IO_sreen_6

Figure IO_screen-2.dialog box demo_inputdlg_02

The listdlg function

If you have a list of options where can be chosen from, listdlg is the solution to go, it is a

powerful function allows the user to select one or more choice(s) from a list of items.

An example of the use of listdlg is given in demo_listdlg_01.m

% prepare the list of options to select fromformat_list = [{'fig - MATLAB figure'}, {'jpg - JPEG'}, ...

{'bmp - Windows bitmap'}, {'emf - Enhanced metafile'}, ...{'eps - EPS Level 1'}, {'m - MATLAB M-file'}, ...{'pbm - Portable bitmap'}, {'pcx - Paintbrush 24-bit'}, ...{'pgm - Portable Graymap'}, {'png - Portable Network Graphics'}, ...{'ppm - Portable Pixmap'}, {'tif - TIFF (kompr.)'}];

[selection, was_OK] = listdlg('PromptString', 'Select file formats to save

pictures:', ...'ListSize', [250 200], 'SelectionMode', 'single', ...'ListString', format_list);



7/20

ICT Onderzoek LUDIT

IO_sreen_7

Figure IO_screen-3. dialog box demo_listdlg_01

The menu function

If a very limited choice of parameters is available to choose from, then the menufunction can be used. The user has only to click on the right button, and the index of its

choice is returned as a result

An example of the use of menu is given in demo_menu_01.m

% ask the user the color of the plotk = menu('Choose a color','Red','Green','Blue');

% select the color depending on the index chosencolor = ['r','g','b'];



8/20

ICT Onderzoek LUDIT

IO_sreen_8

Figure IO_screen-4. menu dialog box demo_menu_01.m

Output to screen

The disp function

Table IO_screen-3. disp function


dispDisplay text or array

disp(X)

displays an array, without printing the

array name. IfX contains a text string, the

string is displayed.

Note that disp does not display empty

arrays.

TIP: A combination of text and variables is possible by concatenation.

A numerical variable has to be transformed into a string first.

An example of the use of menu is given in demo_menu_01.m

% put some text onto the screendisp('This is text');

% put the numerical values onto the screendisp(x);


9/20

ICT Onderzoek LUDIT

IO_sreen_9

% combine some text and numerical values (numerical values have to be% transformed into string formatdisp(['First element= ' num2str(x(1)) ' Last element= ' num2str(x(10))]);

Interactive IO

Several build in dialog boxes are already available in MATLAB. The most interesting are

given in the table below. Check the MATLAB HELP for more on dialog boxes an the

format to use.

Table IO_screen-4. Some interesting built-in dialog boxes


errordlg Create error dialog box

errordlg('errorstring','dlgname','on')

a dialog box named 'dlgname' that contains the string 'errorstring'.

'on' specifies whether to replace an existing dialog box having the

same name. 'on' brings an existing error dialog having the same

name to the foreground.

helpdlg Display help dialog box

helpdlg('helpstring','dlgname')

displays a dialog box named 'dlgname' containing the string

'helpstring'. MATLAB wraps the text in 'helpstring' to fit the width

of the dialog box. The dialog box remains on your screen until you

press the OK button or the Enter key.

questdlg Create question dialog box

button= questdlg('qstring','title','default')

'qstring' is a cell array or a string that automatically wraps to fit

within the dialog box.

'title' is displayed in the dialog's title bar.

The dialog has three default buttons, Yes, No, and Cancel. If the

user presses one of these three buttons, button is set to the name of

the button pressed. If the user presses the close button on the dialog,

button is set to the empty string. If the user presses the Return key,

button is set to 'Yes'.

warndlg Create warning dialog box


10/20

ICT Onderzoek LUDIT

IO_sreen_10


h = warndlg('warnstring','dlgname',createmode)

specifies whether a warning dialog box is modal or non-modal.

Valid values for createmode are 'modal', 'non-modal', and 'replace'.

If createmode is 'modal' or 'replace', the first available warning

dialog box with the specified title is updated to reflect the new

properties of the warning dialog box. All other such warning dialog

boxes are deleted. If createmode is 'non-modal', the warning dialog

box is not replaced and a new handle is created. The default value

for createmode is 'non-modal'.

waitbar Open waitbar

h = waitbar(x,'title')

TIP: When using errordlg, you have to make a choice if you want to

popup error boxes for each error message or if you want to recycle the

error box and have the same box displaying different error messages.

This is done by specifying the third parameter 'on'.

TIP: The default mode of warndlg, will always create a new dialog boxto show a new warning.

TIP: The waitbar command is especially useful, when you have for-

loops in your program, then you can visualise the time passing by.

An example of the use these different interactive dialog boxes is given in

demo_interactivedlg_01.m

while 1

% ask the user to choose from the optionsk_choice = menu('Choose a dialog box','errordlg', 'helpdlg', 'warndlg',

'questdlg', 'waitbar', 'stop');

% use the switchswitch k_choice


11/20

ICT Onderzoek LUDIT

IO_sreen_11

case 1

% the same error dialog box is kept, watch the time changingstr_1 = ['OUCH! This is the right time: ' datestr(now)];errordlg(str_1, 'error_1', 'on');

case 2% the same help dialog box is kept, watch the time changing,

% click ok, to make the box dissappearstr_2 = ['FYI: ' datestr(now)];helpdlg(str_2, 'help_2');

case 3% use an extra inputdlg window to enter data

prompt = { 'enter a number'};dlg_title = 'Data Entry for Problem warning';

defAns = {'4'};% create the dialog box with the inputdlg commandanswer = inputdlg(prompt, dlg_title, 1, defAns);

x = str2num(answer{1});if ((x1))

warndlg('Inadequate range. Value set to 0.5','Input Error')end

case 4% a default 2 button question box is used

answer=questdlg('Do you want to install this software?');if strcmp(answer,'Yes')

license=['LICENSE this software is licensed free of charge for

educational use '];license=questdlg(license,'Do you agree?','No');

end

case 5% the computational loop takes 5 seconds

h = waitbar(0,'Please wait...');for i=1:5,

pause(1);waitbar(i/5)

endclose(h)

case 6break

end

end



12/20

ICT Onderzoek LUDIT

IO_sreen_12

Figure IO_screen-5. Different interactive dialog boxes

Formatted IO

The disp function can be used to put a string onto the screen, if you want the string to

have a specified format, the best way is to build up the string with the sprintf command

and use format specifiers.

The sprintf function

Table IO_screen-5. sprinfcommand


sprintf Write formatted data to string

[s, errmsg] = sprintf(format, variables)

format is the specified format. It consists of a chain of format

specifiers (place holders) variables is the list of variables to print

according to the specified format.

returns

The result is returned in a string variable s. An error message string

errmsg is returned if an error occurred. errmsg is an empty matrix

if no error occurred.

The format specification used in MATLAB is based on the model used inthe C programming language. Format specifiers (starting with %) are used

to build the layout of the string to print.


13/20

ICT Onderzoek LUDIT

IO_sreen_13

format placeholders

Formatting takes place via placeholders within the format string. For example, if a

program prints out a zip code, a prefix could be "ZIP code: ". To denote that an integer

is to be shown immediately after that message, the format string "ZIP code: %d." is used.

Table IO_screen-6. Format specification

specification

'% [flag][width][.precision]type' syntax for a format

placeholder

%-12.5e

Table IO_screen-7.Optional format specifier

Flag Can be optional

+ Will always denote the sign '+' or '-' of a

number (the default is to omit the sign for

positive numbers). Only applicable to

numeric types.

- Will left-align the output of this

placeholder (the default is to right-align the

output).

0 Pad arguments with leading zeros '0'

(instead of spaces) to left fill a fixed length

field.

Width

number Causes to pad the output of this

placeholder with spaces until it is at least

number characters wide. If number has a

leading '0', then padding is done with '0'

characters.

.Precision

number For non-integral numeric types, causes the

decimal portion of the output to be

expressed in at least numberdigits. For the

string type, causes the output to be

truncated at numbercharacters.


14/20

ICT Onderzoek LUDIT

IO_sreen_14

Table IO_screen-8. Type format specifier

Type

c Print a char (character).

d Print an int as a signed decimal number.

E, e rint a double value in standard form ([-

]d.ddd e[+/-]ddd). 'e' uses lower-case

letters, 'E' uses upper-case letters.

f Print a double in normal (fixed-point)

notation.

G, g Print a double in either normal or

exponential notation, whichever is more

appropriate for its magnitude. 'g' uses

lower-case letters, 'G' uses upper-case

letters. This type differs slightly from

fixed-point notation in that insignificant

zeroes to the right of the decimal point are

not included. Also, the decimal point is not

included on whole numbers.

o Print an unsigned int in octal.

s Print a character string.

X, x Print an unsigned int as a

hexadecimal number. 'x' uses lower-case

letters and 'X' uses upper-case.

Table IO_screen-9. Escape sequences

\n New line

\t Horizontal tab

\b Backspace

\r Carriage return

\f Form feed


15/20

ICT Onderzoek LUDIT

IO_sreen_15

\\ print a backslash \ symbol

%% %% print a percent symbol %

Printing a string

Strings will be pritned using the %Ls format specifier. L specifies the length of the string.

The string will be right-aligned (if the string is smaller than L characters). The flag -

will left align the string. If the length is not specified, the length will be equal to the

length of the string variable to be printed.

An example of the string formating is given in demo_format_01.m

% most simple formats = sprintf('Hello world \n');disp(s)

% changing the format - use s typestr_hello = 'Hello world';sprintf('%s',str_hello)

% default right alignmentsprintf('%30s',str_hello)

% left alignmentsprintf('%-30s',str_hello)

% what happens if the specified length is smaller than the string?

% the string will still be printed completelysprintf('%5s',str_hello)

% The "%s" code inserts text in the template.fileName = 'home/assignments/a1.txt';s = sprintf('My first assignment is in the file, "%s" \n', fileName);disp(s)

% digit string specifying the minimum number of digits to be printeds = sprintf('%5c','matlab');disp(s)

s = sprintf('\n');disp(s)

% watch out where to place the new line escape sequence

s = sprintf('%5c \n','matlab');disp(s)


16/20

ICT Onderzoek LUDIT

IO_sreen_16

s = sprintf('%c','matlab');disp(s)s = sprintf('\n');disp(s)


>> demo_format_01

Hello world

ans =

Hello world

ans =

Hello world

ans =

Hello world

ans =

Hello world

My first assignment is in the file, "home/assignments/a1.txt"

m a t l a b

m

a

t

l

a

b

matlab

Printing numbers

A real number will be printed following the %+- L.D type,

format. L is the total length of the printed number

(decimal point included). D is the number of digits to be

printed to the right of the decimal point. The default

alignment is right, putting a - in front will left align.


17/20

ICT Onderzoek LUDIT

IO_sreen_17


% Numbers can be inserted in the text. "%f is a code for insert-% ing a number.

s = sprintf('First number = %f, next number = %f \n', 11, 2/3);disp(s)

% The number of places after the decimal point can be% controlled: "%.2f" produces two digits after the point.s = sprintf('First number = %.2f, next number = %.9f \n', 1/3, 1/3);disp(s)

% the same numer, but printed with the exponential type es = sprintf('First number = %.2e, next number = %.9E \n', 1/3, 1/3);disp(s)

% The special sequence, "\n", starts a new line.s = sprintf(' Pi to 2 places %.2f \n Pi to 12 places %.12f \n', pi,pi);

disp(s)

% The "%e" code displays numbers in scientific notation:s = sprintf(' Pi = %e Million = %e 1/700 = %E \n', pi, 1E6, 1/700);disp(s)

% For more (or fewer) places after the decimal pointX=9.12345678901234E-8;

s = sprintf(' 2 places %.2e; 14 places %.14e \n', X,X);disp(s)

% A digit string including a period (.)

s = sprintf('%10.4f',123.456);disp(s)

% printing 100.35 with different type specifierssprintf('%5g',100.35)sprintf('%d',100.35)

% printing 100 with different type specifierssprintf('%c',100)

sprintf('%s',100)sprintf('%d',100)sprintf('%g',100)sprintf('%6.2f',100)sprintf('%6.2e',100)sprintf('%o',100)



18/20

ICT Onderzoek LUDIT

IO_sreen_18

>> demo_format_02

First number = 11.000000, next number = 0.666667

First number = 0.33, next number = 0.333333333

First number = 3.33e-001, next number = 3.333333333E-001

Pi to 2 places 3.14

Pi to 12 places 3.141592653590

Pi = 3.141593e+000 Million = 1.000000e+006 1/700 = 1.428571E-003

2 places 9.12e-008; 14 places 9.12345678901234e-008

123.4560

ans =

100.35

ans =

1.003500e+002

ans =

d

Warning: The argument for the %s format specifier must be of type char (a string).

> In demo_format_02 at 53

ans =

d

ans =

100

ans =

100

ans =

100.00

ans =

1.00e+002


19/20

ICT Onderzoek LUDIT

IO_sreen_19

ans =

144

TIP : sprintf can be used as a vector command, if the variable is not

a scalar, the format is utilized for the elements of the array (column by

column)


% a vectorx = 1:10;s = sprintf(' %d ,',x);

disp(s)

% a matrix (column wise)x = [1 2; 3 4];s = sprintf(' %d ,',x);

disp(s)

% building a 2-column structure% the data is stored in a vectorz = [];

x = 1:10;for i=1:length(x)

z = [z ,x(i), sin(x(i))];

end;s = sprintf('%04.1f | %+8.6e \n ', z );disp(s)


>> demo_format_03

1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ,

1 , 3 , 2 , 4 ,

01.0 | +8.414710e-001

02.0 | +9.092974e-001

03.0 | +1.411200e-001

04.0 | -7.568025e-001

05.0 | -9.589243e-001

06.0 | -2.794155e-001

07.0 | +6.569866e-001

08.0 | +9.893582e-001

09.0 | +4.121185e-001

10.0 | -5.440211e-001


20/20

ICT Onderzoek LUDIT

IO_sreen_20

The fprintf command is analogous to the sprintf command and is used for a

formatted print into a file.

Documents

Matlab Io Screen