FFT - FAX

SYNOPSIS
     
     CALL SET99  (trigs, ifax, n)
     
     CALL FAX    (ifax, n, 3)
     
     CALL FFTRIG (trigs, n, 3)
     
DESCRIPTION
     
     trigs - real variable of dimension n
     
     ifax  - integer variable of dimension 10
     
     n     - the length of the transforms to be performed. n need not be even
             but must have prime factors 2, 3 and 5 only. The number of words
             of IFAX used increases logarithmically with n. ifax(10) is 
             sufficient for most practical purposes. (Transforms of length
             at least 10000)
     
     
     SET99 returns in trigs an array of trigonometric function values
     subsequently used by FFT routines.
     
     SET99 factorises n into factors of 8,6,5,4,3,2 in ifax (with at most
     one factor of 8). ifax(1) contains the number of factors and the factors
     themselves are stored in ascending order in IFAX(2),IFAX(3)..
     
     Presence of an illegal factor causes an error message to be written
     to unit 6, followed by a RETURN (no abort).
     
IMPLEMENTATION
     
     These routines are available on both systems : UNICOS and
     workstations.