TODO before FFTW-$2\pi$:* Wisdom: make it clear that it is specific to the exact fftw version and configuration. Report error codes when reading wisdom. Maybe have multiple system wisdom files, one per version?* DCT/DST codelets? which kinds?* investigate the addition-chain trig computation* I can't believe that there isn't a closed form for the omega array in Rader.* convolution problem type(s)* Explore the idea of having n < 0 in tensors, possibly to mean inverse DFT.* better estimator: possibly, let "other" cost be coef * n, where coef is a per-solver constant determined via some big numerical optimization/fit.* vector radix, multidimensional codelets* it may be a good idea to unify all those little loops that do copying, (X[i], X[n-i]) <- (X[i] + X[n-i], X[i] - X[n-i]), and multiplication of vectors by twiddle factors.* Pruned FFTs (basically, a vecloop that skips zeros).* Try FFTPACK-style back-and-forth (Stockham) FFT. (We tried this a few years ago and it was slower, but perhaps matters have changed.)* Generate assembly directly for more processors, or maybe fork gcc. =)* ensure that threaded solvers generate (block_size % 4 == 0) to allow SIMD to be used.* memoize triggen.