* Sine and Cosine Transforms from FFTPACK. * A simple multidimensional fft.* Convolutions. This will need different interfaces corresponding tothe type of underlying FFT (radix-2, mixed-radix, radix-2 real,mixed-radix real). The convolution function should be fft'ed beforebeing passed, so that the function can be used in a loop.  The mainpoint of the function being to do the index manipulation for themultiplication F*G.  Theoretically someone might want to convolve realand complex data together which could be done but would double thenumber of interfaces. It would be reasonable to restrict theconvolutions to real-real and complex-complex.