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UBC CS TR-87-19 Summary

Time-Space Tradeoffs for Branching Programs Contrasted With Those for Straight-Line Programs, June 1987 Karl Abrahamson

This paper establishes time-space tradeoffs for some algebraic problems in the branching program model, including convolution of vectors, matrix multiplication, matrix inversion, computing the product of three matrices and computing $PAQ$ where $P$ and $Q$ are permutation matrices. While some of the results agree well with known results for straight- line programs, one of them (for matrix multiplication) surprisingly is stronger, and one (for computing $PAQ$) is necessarily weaker. Some of the tradeoffs are proved for expected time and space, where all inputs are equally likely.


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