Forward transforms

• Increase the size of the work array

  The work array passed to the FFT routine needs to be increased in size from 3*MAXDIM elements (for NAG) to 6*MAXDIM+15 (for FFTPACK). Here, MAXDIM is the size of the largest array dimension.

• Replace call to C06FJF with PDA_DNFFTF

  Replace the call

        DOUBLE PRECISION X(N), Y(N), WORK( 3*MAXDIM )
        INTEGER ND( NDIM )
        CALL C06FJF( NDIM, ND, N, X, Y, WORK, LWORK, IFAIL )
  

  with

        DOUBLE PRECISION X(N), Y(N), WORK( 6*MAXDIM + 15 )
        INTEGER ND( NDIM )
        CALL PDA_DNFFTF( NDIM, ND, X ,Y, WORK, ISTAT )
        IF( ISTAT .NE. 0 ) THEN
           This means that NDIM was either less than 1 or greater than 20.
           Report a programming error!
        END IF