/*****************************************************************************
*                                                                            *
*   FZINTERP.SPL Copyright (C) 1999 DSP Development Corporation              *
*                               All Rights Reserved                          *
*                                                                            *
*   Author:      Randy Race                                                  *
*                                                                            *
*   Synopsis:    Sinx/sin interpolation of periodic band limited waveforms   *
*                                                                            *
*   Revisions:   30 Jun 1999  RRR  Creation - from ZINTERP.MAC               *
*                                                                            *
*****************************************************************************/


#if @HELP_FZINTERP

    FZINTERP

    Purpose: Interpolates a series by a factor using FFT zero insertion

    Syntax:  FZINTERP(s, n)

                   s - input series or array

                   n - real, the interpolation factor, N > 1.0,
                       defaults to 2.0

    Returns: A series or array

    Example:

             W1: gsin(64, 1/64, 3)
             W2: fzinterp(W1, 4)

             W1 contains 64 samples of a 3 Hz sine wave sampled at
             64 Hz.

             W2 produces a 253 point interpolated 3 Hz sine wave with a
             sample rate of 64 * 4 = 256 Hz.


             W3: fzinterp(W1, 3.5)

             produces a 221 point interpolated 3 Hz sinewave with a
             sample rate of 64 * 3.5 = 224 Hz

   Remarks:

             FZINTERP is identical to ZINTERP except that the
             interpolation factor (i.e. the multiple of the original
             sampling rate) is specified instead of the new rate.

             Although the interpolation factor N is NOT required to be
             an integer, for an output length L, the relation:

                        N = L / length(s)

             must hold, so the actual interpolation factor might differ
             from N. See ZINTERP for algorithm details.

    See Also:
             Fsinterp
             Interp
             Polyfit
             Spline
             Zinterp
#endif


/* interpolate by a factor using zero insertion */
fzinterp(s, n)
{
        /* hurdles */
        if (argc < 2)
        {
                if (argc < 1) error("fzinterp - input series required");
                
                n = 2.0;
        }
        
        if (n == 1.0)
        {
                return(s);
        }
        else if (n < 1.0)
        {
                error("fzinterp - n must be > 1");
        }
        else
        {
                return(zinterp(s, n*rate(s)));
        }
}