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Identity Testing for constant-width, and commutative, ROABPs Rohit Gurjar * , Arpita Korwar, Nitin Saxena Aalen University and IIT Kanpur June 1, 2016 * supported by TCS research fellowship supported by DST-SERB Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 1 / 26

Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

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Page 1: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Identity Testing for constant-width, andcommutative, ROABPs

Rohit Gurjar∗, Arpita Korwar, Nitin Saxena†

Aalen University and IIT Kanpur

June 1, 2016

∗supported by TCS research fellowship†supported by DST-SERBGurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 1 / 26

Page 2: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Introduction

Polynomial Identity Testing

PIT: given a polynomial P(x) ∈ F[x1, x2, . . . , xn], P(x) = 0?

Input Models:

Arithmetic CircuitsArithmetic Branching Programs

Figure : An Arithmetic circuit

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 2 / 26

Page 3: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Introduction

Polynomial Identity Testing

PIT: given a polynomial P(x) ∈ F[x1, x2, . . . , xn], P(x) = 0?

Input Models:

Arithmetic CircuitsArithmetic Branching Programs

××

+ x2 − 2xy

x y −2

x2 −2xy

Figure : An Arithmetic circuit

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 2 / 26

Page 4: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Introduction

Randomized Test

Rephrasing the question: Given an arithmetic circuit decide if itcomputes the zero polynomial.

Randomized PIT: evaluate P(x) at a random point[Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980].

There is no efficient deterministic test known.

Two Paradigms:

Whitebox: one can see the input circuit.Blackbox: circuit is hidden, only evaluations are allowed (hitting-sets).

Derandomizing PIT has connections with circuit lower bounds[Kabanets and Impagliazzo, 2003, Agrawal, 2005].

An efficient test is known only for restricted classes of circuits,e.g., Sparse polynomials, set-multilinear circuits, ROABP.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 3 / 26

Page 5: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Introduction

Randomized Test

Rephrasing the question: Given an arithmetic circuit decide if itcomputes the zero polynomial.

Randomized PIT: evaluate P(x) at a random point[Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980].

There is no efficient deterministic test known.

Two Paradigms:

Whitebox: one can see the input circuit.Blackbox: circuit is hidden, only evaluations are allowed (hitting-sets).

Derandomizing PIT has connections with circuit lower bounds[Kabanets and Impagliazzo, 2003, Agrawal, 2005].

An efficient test is known only for restricted classes of circuits,e.g., Sparse polynomials, set-multilinear circuits, ROABP.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 3 / 26

Page 6: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Introduction

Randomized Test

Rephrasing the question: Given an arithmetic circuit decide if itcomputes the zero polynomial.

Randomized PIT: evaluate P(x) at a random point[Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980].

There is no efficient deterministic test known.

Two Paradigms:

Whitebox: one can see the input circuit.Blackbox: circuit is hidden, only evaluations are allowed (hitting-sets).

Derandomizing PIT has connections with circuit lower bounds[Kabanets and Impagliazzo, 2003, Agrawal, 2005].

An efficient test is known only for restricted classes of circuits,e.g., Sparse polynomials, set-multilinear circuits, ROABP.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 3 / 26

Page 7: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Introduction

Randomized Test

Rephrasing the question: Given an arithmetic circuit decide if itcomputes the zero polynomial.

Randomized PIT: evaluate P(x) at a random point[Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980].

There is no efficient deterministic test known.

Two Paradigms:

Whitebox: one can see the input circuit.Blackbox: circuit is hidden, only evaluations are allowed (hitting-sets).

Derandomizing PIT has connections with circuit lower bounds[Kabanets and Impagliazzo, 2003, Agrawal, 2005].

An efficient test is known only for restricted classes of circuits,e.g., Sparse polynomials, set-multilinear circuits, ROABP.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 3 / 26

Page 8: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Introduction

Randomized Test

Rephrasing the question: Given an arithmetic circuit decide if itcomputes the zero polynomial.

Randomized PIT: evaluate P(x) at a random point[Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980].

There is no efficient deterministic test known.

Two Paradigms:

Whitebox: one can see the input circuit.Blackbox: circuit is hidden, only evaluations are allowed (hitting-sets).

Derandomizing PIT has connections with circuit lower bounds[Kabanets and Impagliazzo, 2003, Agrawal, 2005].

An efficient test is known only for restricted classes of circuits,e.g., Sparse polynomials, set-multilinear circuits, ROABP.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 3 / 26

Page 9: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Preliminaries

Arithmetic Branching Programs

−1

x2

s t

x1 + x2 5

x2

x1 + 2x4 x1

Figure : An Arithmetic branching program.

ABP: a directed acyclic graph G with a start node and an end node.

Each edge has a weight from F[x].

C (x) =∑

p∈paths(s,t)

W (p), where W (p) =∏e∈p

W (e).

C (x) = (x1 + 2x4)x2x1 − (x1 + 2x4)x2 + (x1 + x2)5x2

Width: maximum number of nodes in a layer.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 4 / 26

Page 10: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Preliminaries

Arithmetic Branching Programs

−1

x2

s t

x1 + x2 5

x2

x1 + 2x4 x1

Figure : An Arithmetic branching program.

ABP: a directed acyclic graph G with a start node and an end node.

Each edge has a weight from F[x].

C (x) =∑

p∈paths(s,t)

W (p), where W (p) =∏e∈p

W (e).

C (x) = (x1 + 2x4)x2x1 − (x1 + 2x4)x2 + (x1 + x2)5x2

Width: maximum number of nodes in a layer.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 4 / 26

Page 11: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Preliminaries

Arithmetic Branching Programs

−1

x2

s t

x1 + x2 5

x2

x1 + 2x4 x1

Figure : An Arithmetic branching program.

ABP: a directed acyclic graph G with a start node and an end node.

Each edge has a weight from F[x].

C (x) =∑

p∈paths(s,t)

W (p), where W (p) =∏e∈p

W (e).

C (x) = (x1 + 2x4)x2x1 − (x1 + 2x4)x2 + (x1 + x2)5x2

Width: maximum number of nodes in a layer.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 4 / 26

Page 12: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Preliminaries

Arithmetic Branching Programs

−1

x2

s t

x1 + x2 5

x2

x1 + 2x4 x1

Figure : An Arithmetic branching program.

ABP: a directed acyclic graph G with a start node and an end node.

Each edge has a weight from F[x].

C (x) =∑

p∈paths(s,t)

W (p), where W (p) =∏e∈p

W (e).

C (x) = (x1 + 2x4)x2x1 − (x1 + 2x4)x2 + (x1 + x2)5x2

Width: maximum number of nodes in a layer.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 4 / 26

Page 13: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Preliminaries

Arithmetic Branching Programs

−1

x2

s t

x1 + x2 5

x2

x1 + 2x4 x1

Figure : An Arithmetic branching program.

Equivalent representation:[x1 + 2x4 x1 + x2

] [x2 −10 5

] [x1

x2

]

C (x) = (x1 + 2x4)x2x1 − (x1 + 2x4)x2 + (x1 + x2)5x2

Width: maximum dimension of the matrices.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 5 / 26

Page 14: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Preliminaries

Power of ABPs

Almost as powerful as arithmetic circuits[Valiant, 1979, Berkowitz, 1984].

Width-3 ABPs have the same expressive power as arithmeticformulas [Ben-Or and Cleve, 1992].

Deterministic PIT: only for special ABPs, e.g. read-once obliviousABP.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 6 / 26

Page 15: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Preliminaries

Power of ABPs

Almost as powerful as arithmetic circuits[Valiant, 1979, Berkowitz, 1984].

Width-3 ABPs have the same expressive power as arithmeticformulas [Ben-Or and Cleve, 1992].

Deterministic PIT: only for special ABPs, e.g. read-once obliviousABP.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 6 / 26

Page 16: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Preliminaries

Power of ABPs

Almost as powerful as arithmetic circuits[Valiant, 1979, Berkowitz, 1984].

Width-3 ABPs have the same expressive power as arithmeticformulas [Ben-Or and Cleve, 1992].

Deterministic PIT: only for special ABPs, e.g. read-once obliviousABP.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 6 / 26

Page 17: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Oblivious ABP

Read-once Oblivious ABP

Any variable occurs in at most one layer.

4x3 − 3

x3

x2x34 − 1

2x4 + 1

3x1

x21 + 1

2

1 − x3

3x43

x3 + 1

x23 + 5x3

1 − x2

x2 + 3x22

x4

2x31 + 3

Figure : A Read-once oblivious ABP with variable order (x1, x3, x2, x4)

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 7 / 26

Page 18: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Oblivious ABP

PIT for ROABPs

[Raz and Shpilka, 2005] gave a polynomial time whitebox test forROABP.

Blackbox test: nO(log n) time[Forbes and Shpilka, 2013, Forbes et al., 2014, Agrawal et al., 2015].

Nothing better known even for constant width.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 8 / 26

Page 19: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Oblivious ABP

PIT for ROABPs

[Raz and Shpilka, 2005] gave a polynomial time whitebox test forROABP.

Blackbox test: nO(log n) time[Forbes and Shpilka, 2013, Forbes et al., 2014, Agrawal et al., 2015].

Nothing better known even for constant width.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 8 / 26

Page 20: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Oblivious ABP

PIT for ROABPs

[Raz and Shpilka, 2005] gave a polynomial time whitebox test forROABP.

Blackbox test: nO(log n) time[Forbes and Shpilka, 2013, Forbes et al., 2014, Agrawal et al., 2015].

Nothing better known even for constant width.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 8 / 26

Page 21: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Oblivious ABP

Our Results

1 Polynomial time blackbox test for constant width ROABPs*.

* known variable order.* zero characteristic field (or large enough).

2 Commutative ROABP: where matrices commute (no variable order).

dO(log w)(nw)O(log log w)-time blackbox test [Forbes et al., 2014]

– for n variables, width w and individual degree d .

We improve it to (dnw)O(log log w)-time.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 9 / 26

Page 22: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Oblivious ABP

Our Results

1 Polynomial time blackbox test for constant width ROABPs*.

* known variable order.* zero characteristic field (or large enough).

2 Commutative ROABP: where matrices commute (no variable order).

dO(log w)(nw)O(log log w)-time blackbox test [Forbes et al., 2014]

– for n variables, width w and individual degree d .

We improve it to (dnw)O(log log w)-time.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 9 / 26

Page 23: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Oblivious ABP

Our Results

1 Polynomial time blackbox test for constant width ROABPs*.

* known variable order.* zero characteristic field (or large enough).

2 Commutative ROABP: where matrices commute (no variable order).

dO(log w)(nw)O(log log w)-time blackbox test [Forbes et al., 2014]

– for n variables, width w and individual degree d .

We improve it to (dnw)O(log log w)-time.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 9 / 26

Page 24: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Oblivious ABP

Our Results

1 Polynomial time blackbox test for constant width ROABPs*.

* known variable order.* zero characteristic field (or large enough).

2 Commutative ROABP: where matrices commute (no variable order).

dO(log w)(nw)O(log log w)-time blackbox test [Forbes et al., 2014]

– for n variables, width w and individual degree d .

We improve it to (dnw)O(log log w)-time.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 9 / 26

Page 25: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Oblivious ABP

Our Results

1 Polynomial time blackbox test for constant width ROABPs*.

* known variable order.* zero characteristic field (or large enough).

2 Commutative ROABP: where matrices commute (no variable order).

dO(log w)(nw)O(log log w)-time blackbox test [Forbes et al., 2014]

– for n variables, width w and individual degree d .

We improve it to (dnw)O(log log w)-time.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 9 / 26

Page 26: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Ordered Branching Programs

Read-once Ordered Branching Programs

x1 = 0

x1 = 1

x2 = 0

x2 = 1

x2 = 1

x3 = 0

x3 = 1

x3 = 1

x4 = 0

x4 = 1

x2 = 0

x4 = 0

x3 = 1

x3 = 0

Figure : An ROBP

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 10 / 26

Page 27: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Ordered Branching Programs

Pseudorandomness for ROBP

Comes from the RL versus L question.

A distribution is pseudorandom if any ROBP cannot distinguish itfrom the uniform random distribution.

Goal: construct a PRG with O(log n) seed length (polynomial sizesample space).

Best known result: O(log2 n) seed length[Nisan, 1990, Impagliazzo et al., 1994, Raz and Reingold, 1999].

Nothing better known even for constant width.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 11 / 26

Page 28: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Ordered Branching Programs

Pseudorandomness for ROBP

Comes from the RL versus L question.

A distribution is pseudorandom if any ROBP cannot distinguish itfrom the uniform random distribution.

Goal: construct a PRG with O(log n) seed length (polynomial sizesample space).

Best known result: O(log2 n) seed length[Nisan, 1990, Impagliazzo et al., 1994, Raz and Reingold, 1999].

Nothing better known even for constant width.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 11 / 26

Page 29: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Ordered Branching Programs

Pseudorandomness for ROBP

Comes from the RL versus L question.

A distribution is pseudorandom if any ROBP cannot distinguish itfrom the uniform random distribution.

Goal: construct a PRG with O(log n) seed length (polynomial sizesample space).

Best known result: O(log2 n) seed length[Nisan, 1990, Impagliazzo et al., 1994, Raz and Reingold, 1999].

Nothing better known even for constant width.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 11 / 26

Page 30: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Ordered Branching Programs

Pseudorandomness for ROBP

Comes from the RL versus L question.

A distribution is pseudorandom if any ROBP cannot distinguish itfrom the uniform random distribution.

Goal: construct a PRG with O(log n) seed length (polynomial sizesample space).

Best known result: O(log2 n) seed length[Nisan, 1990, Impagliazzo et al., 1994, Raz and Reingold, 1999].

Nothing better known even for constant width.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 11 / 26

Page 31: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Ordered Branching Programs

Pseudorandomness for ROBP

Comes from the RL versus L question.

A distribution is pseudorandom if any ROBP cannot distinguish itfrom the uniform random distribution.

Goal: construct a PRG with O(log n) seed length (polynomial sizesample space).

Best known result: O(log2 n) seed length[Nisan, 1990, Impagliazzo et al., 1994, Raz and Reingold, 1999].

Nothing better known even for constant width.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 11 / 26

Page 32: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Ordered Branching Programs

[Impagliazzo et al., 1994]

PRG

r bits r bits

r + O(log w) bits

Sample space size: poly(w)× 2r instead of trivial 2r × 2r .

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 12 / 26

Page 33: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Read-once Ordered Branching Programs

[Impagliazzo et al., 1994]

PRG

r bits r bits

r + O(log w) bits

Sample space size: poly(w)× 2r instead of trivial 2r × 2r .

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 12 / 26

Page 34: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Hitting-set for Bivariate ROABP

g1(x1)

g2(x1) h2(x2)

hw (x2)gw (x1)

h1(x2)

.

.

.

f (x1, x2) =w∑r=1

gr (x1) hr (x2)

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 13 / 26

Page 35: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Hitting-set for Bivariate ROABP

HSG

g1(x1)

g2(x1) h2(x2)

hw (x2)gw (x1)

h1(x2)

.

.

.

tw tw + tw−1

t

f (x1, x2) =∑w

r=1 gr (x1) hr (x2)

Claim: f (tw , tw + tw−1) 6= 0.

Degree= 2wd , where deg(gr ), deg(hr ) = d .

Hitting-set size: 2wd + 1, instead of trivial (d + 1)× (d + 1).

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 14 / 26

Page 36: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Hitting-set for Bivariate ROABP

HSG

g1(x1)

g2(x1) h2(x2)

hw (x2)gw (x1)

h1(x2)

.

.

.

tw tw + tw−1

t

f (x1, x2) =∑w

r=1 gr (x1) hr (x2)

Claim: f (tw , tw + tw−1) 6= 0.

Degree= 2wd , where deg(gr ), deg(hr ) = d .

Hitting-set size: 2wd + 1, instead of trivial (d + 1)× (d + 1).

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 14 / 26

Page 37: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Hitting-set for Bivariate ROABP

HSG

g1(x1)

g2(x1) h2(x2)

hw (x2)gw (x1)

h1(x2)

.

.

.

tw tw + tw−1

t

f (x1, x2) =∑w

r=1 gr (x1) hr (x2)

Claim: f (tw , tw + tw−1) 6= 0.

Degree= 2wd , where deg(gr ), deg(hr ) = d .

Hitting-set size: 2wd + 1, instead of trivial (d + 1)× (d + 1).

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 14 / 26

Page 38: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Hitting-set for Bivariate ROABP

HSG

g1(x1)

g2(x1) h2(x2)

hw (x2)gw (x1)

h1(x2)

.

.

.

tw tw + tw−1

t

f (x1, x2) =∑w

r=1 gr (x1) hr (x2)

Claim: f (tw , tw + tw−1) 6= 0.

Degree= 2wd , where deg(gr ), deg(hr ) = d .

Hitting-set size: 2wd + 1, instead of trivial (d + 1)× (d + 1).

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 14 / 26

Page 39: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f =[

x1

] x2

x3

· · · xn−1

xn

Claim: f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

Proof: treat x3, x4, . . . , xn as constants.

f =[

x1

] x2

f =

w∑r=1

gr (x1) hr (x2, x3, . . . , xn)

f (tw1 , tw1 + tw−11 ) 6= 0 (bivariate ROABP).

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 15 / 26

Page 40: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f =[

x1

] x2

x3

· · · xn−1

xn

Claim: f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

Proof: treat x3, x4, . . . , xn as constants.

f =[

x1

] x2

f =

w∑r=1

gr (x1) hr (x2, x3, . . . , xn)

f (tw1 , tw1 + tw−11 ) 6= 0 (bivariate ROABP).

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 15 / 26

Page 41: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f =[

x1

] x2

x3

· · · xn−1

xn

Claim: f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

Proof: treat x3, x4, . . . , xn as constants.

f =[

x1

] x2

f =

w∑r=1

gr (x1) hr (x2, x3, . . . , xn)

f (tw1 , tw1 + tw−11 ) 6= 0 (bivariate ROABP).

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 15 / 26

Page 42: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f =[

x1

] x2

x3

· · · xn−1

xn

Claim: f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

Proof: treat x3, x4, . . . , xn as constants.

f =[

x1

] x2

f =

w∑r=1

gr (x1) hr (x2, x3, . . . , xn)

f (tw1 , tw1 + tw−11 ) 6= 0 (bivariate ROABP).

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 15 / 26

Page 43: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f =[

x1

] x2

x3

· · · xn−1

xn

Claim: f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

Proof: treat x3, x4, . . . , xn as constants.

f =[

x1

] x2

f =

w∑r=1

gr (x1) hr (x2, x3, . . . , xn)

f (tw1 , tw1 + tw−11 ) 6= 0 (bivariate ROABP).

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 15 / 26

Page 44: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , twn/2, twn/2 + tw−1

n/2 ) 6= 0.

no. of variables = n→ n/2, individual degree = d → 2wd .

Repeat log n times. 1 variable, indvidual degree = (2w)log nd .

Hitting-set size: O(ndw log n).

Hitting-set size: poly(n, d), if w is constant.

Known variable order.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 16 / 26

Page 45: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , twn/2, twn/2 + tw−1

n/2 ) 6= 0.

no. of variables = n→ n/2, individual degree = d → 2wd .

Repeat log n times. 1 variable, indvidual degree = (2w)log nd .

Hitting-set size: O(ndw log n).

Hitting-set size: poly(n, d), if w is constant.

Known variable order.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 16 / 26

Page 46: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , twn/2, twn/2 + tw−1

n/2 ) 6= 0.

no. of variables = n→ n/2, individual degree = d → 2wd .

Repeat log n times. 1 variable, indvidual degree = (2w)log nd .

Hitting-set size: O(ndw log n).

Hitting-set size: poly(n, d), if w is constant.

Known variable order.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 16 / 26

Page 47: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , twn/2, twn/2 + tw−1

n/2 ) 6= 0.

f ′ =[

t1

] t1

t2

· · · tn/2

tn/2

no. of variables = n→ n/2, individual degree = d → 2wd .

Repeat log n times. 1 variable, indvidual degree = (2w)log nd .

Hitting-set size: O(ndw log n).

Hitting-set size: poly(n, d), if w is constant.

Known variable order.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 16 / 26

Page 48: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , twn/2, twn/2 + tw−1

n/2 ) 6= 0.

f ′ =[

t1

] t2

· · ·tn/2

no. of variables = n→ n/2, individual degree = d → 2wd .

Repeat log n times. 1 variable, indvidual degree = (2w)log nd .

Hitting-set size: O(ndw log n).

Hitting-set size: poly(n, d), if w is constant.

Known variable order.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 16 / 26

Page 49: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , twn/2, twn/2 + tw−1

n/2 ) 6= 0.

f ′ =[

t1

] t2

· · ·tn/2

no. of variables = n→ n/2, individual degree = d → 2wd .

Repeat log n times. 1 variable, indvidual degree = (2w)log nd .

Hitting-set size: O(ndw log n).

Hitting-set size: poly(n, d), if w is constant.

Known variable order.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 16 / 26

Page 50: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , twn/2, twn/2 + tw−1

n/2 ) 6= 0.

f ′ =[

t1

] t2

· · ·tn/2

no. of variables = n→ n/2, individual degree = d → 2wd .

Repeat log n times. 1 variable, indvidual degree = (2w)log nd .

Hitting-set size: O(ndw log n).

Hitting-set size: poly(n, d), if w is constant.

Known variable order.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 16 / 26

Page 51: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , twn/2, twn/2 + tw−1

n/2 ) 6= 0.

f ′ =[

t1

] t2

· · ·tn/2

no. of variables = n→ n/2, individual degree = d → 2wd .

Repeat log n times. 1 variable, indvidual degree = (2w)log nd .

Hitting-set size: O(ndw log n).

Hitting-set size: poly(n, d), if w is constant.

Known variable order.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 16 / 26

Page 52: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , twn/2, twn/2 + tw−1

n/2 ) 6= 0.

f ′ =[

t1

] t2

· · ·tn/2

no. of variables = n→ n/2, individual degree = d → 2wd .

Repeat log n times. 1 variable, indvidual degree = (2w)log nd .

Hitting-set size: O(ndw log n).

Hitting-set size: poly(n, d), if w is constant.

Known variable order.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 16 / 26

Page 53: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

n-variate ROABP

f (tw1 , tw1 + tw−11 , x3, x4, . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , xn) 6= 0.

f (tw1 , tw1 + tw−11 , tw2 , tw2 + tw−1

2 , . . . , twn/2, twn/2 + tw−1

n/2 ) 6= 0.

f ′ =[

t1

] t2

· · ·tn/2

no. of variables = n→ n/2, individual degree = d → 2wd .

Repeat log n times. 1 variable, indvidual degree = (2w)log nd .

Hitting-set size: O(ndw log n).

Hitting-set size: poly(n, d), if w is constant.

Known variable order.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 16 / 26

Page 54: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

Claim: If f (x , y) =∑w

r=1 gr (x)hr (y), then f (tw , tw + tw−1) 6= 0.

Coefficient Matrix for f (x , y) [Nisan, 1991]

y0 · · · y j · · · yd

x0

...x i

...xd

|

− coeff (x iy j)

Define rank(f ) as the rank of this matrix.

Claim: rank(f ) ≤ w [Nisan, 1991].

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 17 / 26

Page 55: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

Claim: If f (x , y) =∑w

r=1 gr (x)hr (y), then f (tw , tw + tw−1) 6= 0.

Coefficient Matrix for f (x , y) [Nisan, 1991]

y0 · · · y j · · · yd

x0

...x i

...xd

|

− coeff (x iy j)

Define rank(f ) as the rank of this matrix.

Claim: rank(f ) ≤ w [Nisan, 1991].

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 17 / 26

Page 56: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

Claim: If f (x , y) =∑w

r=1 gr (x)hr (y), then f (tw , tw + tw−1) 6= 0.

Coefficient Matrix for f (x , y) [Nisan, 1991]

y0 · · · y j · · · yd

x0

...x i

...xd

|

− coeff (x iy j)

Define rank(f ) as the rank of this matrix.

Claim: rank(f ) ≤ w [Nisan, 1991].

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 17 / 26

Page 57: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

Claim: If f (x , y) =∑w

r=1 gr (x)hr (y), then f (tw , tw + tw−1) 6= 0.

Coefficient Matrix for f (x , y) [Nisan, 1991]

y0 · · · y j · · · yd

x0

...x i

...xd

|

− coeff (x iy j)

Define rank(f ) as the rank of this matrix.

Claim: rank(f ) ≤ w [Nisan, 1991].

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 17 / 26

Page 58: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

Define fr = gr (x)hr (y).

Claim: rank(fr ) ≤ 1.

Let gr = a0x0 + a1x

1 + · · ·+ adxd and hr = b0y

0 + b1y1 + · · ·+ bdy

d .

y0 y1 · · · yd

x0

x1

...xd

a0b0 a0b1 a0bda1b0 a1b1 a1bd

...... · · ·

...adb0 adb1 adbd

=⇒ rank(f ) = rank(

∑wr=1 fr ) ≤ w .

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 18 / 26

Page 59: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

Define fr = gr (x)hr (y).

Claim: rank(fr ) ≤ 1.

Let gr = a0x0 + a1x

1 + · · ·+ adxd and hr = b0y

0 + b1y1 + · · ·+ bdy

d .

y0 y1 · · · yd

x0

x1

...xd

a0b0 a0b1 a0bda1b0 a1b1 a1bd

...... · · ·

...adb0 adb1 adbd

=⇒ rank(f ) = rank(∑w

r=1 fr ) ≤ w .

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 18 / 26

Page 60: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

Define fr = gr (x)hr (y).

Claim: rank(fr ) ≤ 1.

Let gr = a0x0 + a1x

1 + · · ·+ adxd and hr = b0y

0 + b1y1 + · · ·+ bdy

d .

y0 y1 · · · yd

x0

x1

...xd

a0b0 a0b1 a0bda1b0 a1b1 a1bd

...... · · ·

...adb0 adb1 adbd

=⇒ rank(f ) = rank(

∑wr=1 fr ) ≤ w .

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 18 / 26

Page 61: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

(x , y) 7→ (tw , tw + tw−1) = (tw , tw (1 + t−1)).

x iy j 7→ t(i+j)w (1 + t−1)j .

leading-term(x iy j) = t(i+j)w .

Same for all x iy j with i + j = `.

i + j = ` − 1

y0 y1

x0

x1

xd

· · ·

.

.

.

yd

i + j = `

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 19 / 26

Page 62: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

(x , y) 7→ (tw , tw + tw−1) = (tw , tw (1 + t−1)).

x iy j 7→ t(i+j)w (1 + t−1)j .

leading-term(x iy j) = t(i+j)w .

Same for all x iy j with i + j = `.

i + j = ` − 1

y0 y1

x0

x1

xd

· · ·

.

.

.

yd

i + j = `

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 19 / 26

Page 63: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

(x , y) 7→ (tw , tw + tw−1) = (tw , tw (1 + t−1)).

x iy j 7→ t(i+j)w (1 + t−1)j .

leading-term(x iy j) = t(i+j)w .

Same for all x iy j with i + j = `.

i + j = ` − 1

y0 y1

x0

x1

xd

· · ·

.

.

.

yd

i + j = `

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 19 / 26

Page 64: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

(x , y) 7→ (tw , tw + tw−1) = (tw , tw (1 + t−1)).

x iy j 7→ t(i+j)w (1 + t−1)j .

leading-term(x iy j) = t(i+j)w .

Same for all x iy j with i + j = `.

i + j = ` − 1

y0 y1

x0

x1

xd

· · ·

.

.

.

yd

i + j = `

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 19 / 26

Page 65: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

(x , y) 7→ (tw , tw + tw−1) = (tw , tw (1 + t−1)).

x iy j 7→ t(i+j)w (1 + t−1)j .

leading-term(x iy j) = t(i+j)w .

Same for all x iy j with i + j = `.

i + j = ` − 1

y0 y1

x0

x1

xd

· · ·

.

.

.

yd

i + j = `

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 19 / 26

Page 66: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

y0 y1

x0

x1

xd

· · ·

.

.

.

yd

i + j = `

0

0

0

0 0

...

Leading nonzero Diagonal: at most w nonzero entries.

Leading term: tw`.

Leading term from the next diagonal: tw(`−1).

Focus on terms {tw`, tw`−1, · · · , tw(`−1)+1}.They come only from an `-th diagonal monomial.

`-th diagonal nonzero monomials: {x`−j1y j1 , x`−j2y j2 , · · · , x`−jw y jw }.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 20 / 26

Page 67: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

y0 y1

x0

x1

xd

· · ·

.

.

.

yd

i + j = `

0

0

0

0 0

...

Leading nonzero Diagonal: at most w nonzero entries.

Leading term: tw`.

Leading term from the next diagonal: tw(`−1).

Focus on terms {tw`, tw`−1, · · · , tw(`−1)+1}.They come only from an `-th diagonal monomial.

`-th diagonal nonzero monomials: {x`−j1y j1 , x`−j2y j2 , · · · , x`−jw y jw }.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 20 / 26

Page 68: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

y0 y1

x0

x1

xd

· · ·

.

.

.

yd

i + j = `

0

0

0

0 0

...

Leading nonzero Diagonal: at most w nonzero entries.

Leading term: tw`.

Leading term from the next diagonal: tw(`−1).

Focus on terms {tw`, tw`−1, · · · , tw(`−1)+1}.They come only from an `-th diagonal monomial.

`-th diagonal nonzero monomials: {x`−j1y j1 , x`−j2y j2 , · · · , x`−jw y jw }.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 20 / 26

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Hitting-set for ROABP

Proof of the bivariate case

y0 y1

x0

x1

xd

· · ·

.

.

.

yd

i + j = `

0

0

0

0 0

...

i + j = ` − 1

Leading nonzero Diagonal: at most w nonzero entries.

Leading term: tw`.

Leading term from the next diagonal: tw(`−1).

Focus on terms {tw`, tw`−1, · · · , tw(`−1)+1}.They come only from an `-th diagonal monomial.

`-th diagonal nonzero monomials: {x`−j1y j1 , x`−j2y j2 , · · · , x`−jw y jw }.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 20 / 26

Page 70: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

y0 y1

x0

x1

xd

· · ·

.

.

.

yd

i + j = `

0

0

0

0 0

...

Leading nonzero Diagonal: at most w nonzero entries.

Leading term: tw`.

Leading term from the next diagonal: tw(`−1).

Focus on terms {tw`, tw`−1, · · · , tw(`−1)+1}.

They come only from an `-th diagonal monomial.

`-th diagonal nonzero monomials: {x`−j1y j1 , x`−j2y j2 , · · · , x`−jw y jw }.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 20 / 26

Page 71: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

y0 y1

x0

x1

xd

· · ·

.

.

.

yd

i + j = `

0

0

0

0 0

...

Leading nonzero Diagonal: at most w nonzero entries.

Leading term: tw`.

Leading term from the next diagonal: tw(`−1).

Focus on terms {tw`, tw`−1, · · · , tw(`−1)+1}.They come only from an `-th diagonal monomial.

`-th diagonal nonzero monomials: {x`−j1y j1 , x`−j2y j2 , · · · , x`−jw y jw }.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 20 / 26

Page 72: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

y0 y1

x0

x1

xd

· · ·

.

.

.

yd

i + j = `

0

0

0

0 0

...

Leading nonzero Diagonal: at most w nonzero entries.

Leading term: tw`.

Leading term from the next diagonal: tw(`−1).

Focus on terms {tw`, tw`−1, · · · , tw(`−1)+1}.They come only from an `-th diagonal monomial.

`-th diagonal nonzero monomials: {x`−j1y j1 , x`−j2y j2 , · · · , x`−jw y jw }.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 20 / 26

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Hitting-set for ROABP

Proof of the bivariate case

(x , y) 7→ (tw , tw (1 + t−1)).

x`−j1y j1 7→ t`w (1 + t−1)j1 .

x`−j1y j1 7→ t`w((

j10

)+

(j11

)t−1 + · · ·+

(j1j1

)t−j1

).

x`−j1y j1 7→(j10

)t`w +

(j11

)t`w−1 + · · ·+

(j1

w − 1

)t(`−1)w+1 + · · ·

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 21 / 26

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Hitting-set for ROABP

Proof of the bivariate case

(x , y) 7→ (tw , tw (1 + t−1)).

x`−j1y j1 7→ t`w (1 + t−1)j1 .

x`−j1y j1 7→ t`w((

j10

)+

(j11

)t−1 + · · ·+

(j1j1

)t−j1

).

x`−j1y j1 7→(j10

)t`w +

(j11

)t`w−1 + · · ·+

(j1

w − 1

)t(`−1)w+1 + · · ·

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 21 / 26

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Hitting-set for ROABP

Proof of the bivariate case

(x , y) 7→ (tw , tw (1 + t−1)).

x`−j1y j1 7→ t`w (1 + t−1)j1 .

x`−j1y j1 7→ t`w((

j10

)+

(j11

)t−1 + · · ·+

(j1j1

)t−j1

).

x`−j1y j1 7→(j10

)t`w +

(j11

)t`w−1 + · · ·+

(j1

w − 1

)t(`−1)w+1 + · · ·

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 21 / 26

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Hitting-set for ROABP

Proof of the bivariate case

x`−j1y j1 7→(j1

0

)t`w +

(j11

)t`w−1 + · · ·+

( j1w−1

)t(`−1)w+1 + · · ·

x`−j2y j2 7→(j2

0

)t`w +

(j21

)t`w−1 + · · ·+

( j2w−1

)t(`−1)w+1 + · · ·

...

x`−jw y jw 7→(jw

0

)t`w +

(jw1

)t`w−1 + · · ·+

( jww−1

)t(`−1)w+1 + · · ·

0 ∗ · · · 0

Assuming jk 6= jk ′ requires nonzero characteristic.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 22 / 26

Page 77: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

x`−j1y j1 7→(j1

0

)t`w +

(j11

)t`w−1 + · · ·+

( j1w−1

)t(`−1)w+1 + · · ·

x`−j2y j2 7→(j2

0

)t`w +

(j21

)t`w−1 + · · ·+

( j2w−1

)t(`−1)w+1 + · · ·

...

x`−jw y jw 7→(jw

0

)t`w +

(jw1

)t`w−1 + · · ·+

( jww−1

)t(`−1)w+1 + · · ·

0 ∗ · · · 0

Assuming jk 6= jk ′ requires nonzero characteristic.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 22 / 26

Page 78: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

x`−j1y j1 7→(j1

0

)t`w +

(j11

)t`w−1 + · · ·+

( j1w−1

)t(`−1)w+1 + · · ·

x`−j2y j2 7→(j2

0

)t`w +

(j21

)t`w−1 + · · ·+

( j2w−1

)t(`−1)w+1 + · · ·

...

x`−jw y jw 7→(jw

0

)t`w +

(jw1

)t`w−1 + · · ·+

( jww−1

)t(`−1)w+1 + · · ·

0 ∗ · · · 0

Assuming jk 6= jk ′ requires nonzero characteristic.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 22 / 26

Page 79: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

x`−j1y j1 7→(j1

0

)t`w +

(j11

)t`w−1 + · · ·+

( j1w−1

)t(`−1)w+1 + · · ·

x`−j2y j2 7→(j2

0

)t`w +

(j21

)t`w−1 + · · ·+

( j2w−1

)t(`−1)w+1 + · · ·

...

x`−jw y jw 7→(jw

0

)t`w +

(jw1

)t`w−1 + · · ·+

( jww−1

)t(`−1)w+1 + · · ·

0 ∗ · · · 0

Assuming jk 6= jk ′ requires nonzero characteristic.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 22 / 26

Page 80: Identity Testing for constant-width, and commutative, ROABPscomputationalcomplexity.org/Archive/2016/slides/... · [Demillo and Lipton, 1978, Zippel, 1979, Schwartz, 1980]. There

Hitting-set for ROABP

Proof of the bivariate case

x`−j1y j1 7→(j1

0

)t`w +

(j11

)t`w−1 + · · ·+

( j1w−1

)t(`−1)w+1 + · · ·

x`−j2y j2 7→(j2

0

)t`w +

(j21

)t`w−1 + · · ·+

( j2w−1

)t(`−1)w+1 + · · ·

...

x`−jw y jw 7→(jw

0

)t`w +

(jw1

)t`w−1 + · · ·+

( jww−1

)t(`−1)w+1 + · · ·

0 ∗ · · · 0

Assuming jk 6= jk ′ requires nonzero characteristic.

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 22 / 26

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Conclusion

Discussion

Possible improvements:

Unknown variable orderHitting-set for all fields.Poly-time for arbitrary width.

Connections between arithmetic and boolean pseudorandomness?

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 23 / 26

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Conclusion

Discussion

Possible improvements:

Unknown variable orderHitting-set for all fields.Poly-time for arbitrary width.

Connections between arithmetic and boolean pseudorandomness?

Gurjar, Korwar, Saxena PIT for constant-width ROABPs June 1, 2016 23 / 26

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