🚀 go-pugleaf

An *excellent* book for numerical analyses is

        Press, W.H., Flannery, B.P., Teukolsky, S.A., and Vetterling,W.T.
        (1989).  Numerical Recipes:  The Art of Scientific Computing,
        Cambridge Unversity Press.

I use the FORTRAN version, which can easily be translated into BASIC.  I
believe that a BASIC version has been published, but I have not looked at
it yet.

Note:   Since the FFT is a convoluted (pun intended) algorithm, many 
        algorithms have errors in them, including the one in Numerical
        Recipes.  If you use the FORTRAN version, the algorithm has the
        line

                WPI = DSIN(THETA)

        This should be 

                WPI = -DSIN(THETA)

        This error will give you problems if you have a complex data set.

        I will post an algorithm that I wrote for a real (not complex) data
        set.  The algorithm is based on that by Press et al.

  kwj