4 research outputs found
Generating and Searching Families of FFT Algorithms
A fundamental question of longstanding theoretical interest is to prove the
lowest exact count of real additions and multiplications required to compute a
power-of-two discrete Fourier transform (DFT). For 35 years the split-radix
algorithm held the record by requiring just 4n log n - 6n + 8 arithmetic
operations on real numbers for a size-n DFT, and was widely believed to be the
best possible. Recent work by Van Buskirk et al. demonstrated improvements to
the split-radix operation count by using multiplier coefficients or "twiddle
factors" that are not n-th roots of unity for a size-n DFT. This paper presents
a Boolean Satisfiability-based proof of the lowest operation count for certain
classes of DFT algorithms. First, we present a novel way to choose new yet
valid twiddle factors for the nodes in flowgraphs generated by common
power-of-two fast Fourier transform algorithms, FFTs. With this new technique,
we can generate a large family of FFTs realizable by a fixed flowgraph. This
solution space of FFTs is cast as a Boolean Satisfiability problem, and a
modern Satisfiability Modulo Theory solver is applied to search for FFTs
requiring the fewest arithmetic operations. Surprisingly, we find that there
are FFTs requiring fewer operations than the split-radix even when all twiddle
factors are n-th roots of unity.Comment: Preprint submitted on March 28, 2011, to the Journal on
Satisfiability, Boolean Modeling and Computatio
PI DEGREE PARITY IN q-SKEW POLYNOMIAL RINGS
For k a field of arbitrary characteristic, and R a k-algebra, we show that the PI degree of an iterated skew polynomial ring R[x1; τ1, δ1] · · · [xn; τn, δn] agrees with the PI degree of R[x1; τ1] · · ·[xn; τn] when each (τi, δi) satisfies a qi-skew relation for qi ∈ k × and extends to a higher qi-skew τi-derivation. We confirm the quantum Gel’fand-Kirillov conjecture for various quantized coordinate rings, and calculate their PI degrees. We extend these results to completely prime factor algebras