Annual review of computer science: vol. 3, 1988
Lower bounds for non-commutative computation
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Lower Bounds and Separations for Constant Depth Multilinear Circuits
CCC '08 Proceedings of the 2008 IEEE 23rd Annual Conference on Computational Complexity
Multi-linear formulas for permanent and determinant are of super-polynomial size
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A Lower Bound for the Size of Syntactically Multilinear Arithmetic Circuits
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Relationless Completeness and Separations
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Homogeneous Formulas and Symmetric Polynomials
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Boolean Function Complexity: Advances and Frontiers
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Arithmetic Circuits: A survey of recent results and open questions
Foundations and Trends® in Theoretical Computer Science
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We initiate a direction for proving lower bounds on the size of non-commutative arithmetic circuits. This direction is based on a connection between lower bounds on the size of non-commutative arithmetic circuits and a problem about commutative degree four polynomials, the classical sum-of-squares problem: find the smallest n such that there exists an identity (x12+x22+•• + xk2)• (y1^2+y22+•• + yk2)= f12+f22+ ... +fn2, where each fi = fi(X,Y) is bilinear in X={x1,... ,xk} and Y={y1,..., yk}. Over the complex numbers, we show that a sufficiently strong super-linear lower bound on n in, namely, n ≥ k1+ε with ε 0, implies an exponential lower bound on the size of arithmetic circuits computing the non-commutative permanent. More generally, we consider such sum-of-squares identities for any M polynomial h(X,Y), namely: h(X,Y) = f12+f22+...+fn2. Again, proving n ≥ k1+ε in for any explicit h over the complex numbers gives an exponential lower bound for the non-commutative permanent. Our proofs relies on several new structure theorems for non-commutative circuits, as well as a non-commutative analog of Valiant's completeness of the permanent. We proceed to prove such super-linear bounds in some restricted cases. We prove that n ≥ Ω(k6/5) in (1), if f1,..., fn are required to have integer coefficients. Over the real numbers, we construct an explicit M polynomial h such that n in (2) must be at least Ω(k2). Unfortunately, these results do not imply circuit lower bounds. We also present other structural results about non-commutative arithmetic circuits. We show that any non-commutative circuit computing an ordered non-commutative polynomial can be efficiently transformed to a syntactically multilinear circuit computing that polynomial. The permanent, for example, is ordered. Hence, lower bounds on the size of syntactically multilinear circuits computing the permanent imply unrestricted non-commutative lower bounds. We also prove an exponential lower bound on the size of non-commutative syntactically multilinear circuit computing an explicit polynomial. This polynomial is, however, not ordered and an unrestricted circuit lower bound does not follow.