Identity Testing and Lower Bounds for Read-k Oblivious Algebraic Branching Programs

Read-k oblivious algebraic branching programs are a natural generalization of the well-studied model of read-once oblivious algebraic branching program (ROABPs). In this work, we give an exponential lower bound of exp(n/k (k)) on the width of any read-k oblivious ABP computing some explicit multilinear polynomial f that is computed by a polynomial size depth-3 circuit. We also study the polynomial identity testing (PIT) problem for this model and obtain a white-box xsubexponential-time PIT algorithm. The algorithm runs in time 2 (1 1/2k-i) and needs white box access only to know the order in which the variables appear in the ABP.