/*****************************************************************************
*                                                                            *
*   CHEBWIN.SPL  Copyright (C) 2012 DSP Development Corporation              *
*                               All Rights Reserved                          *
*                                                                            *
*   Author:      Randy Race                                                  *
*                                                                            *
*   Synopsis:    Multiplies a series with a Dolph-Chebyshev window           *
*                                                                            *
*   Revisions:    6 Jan 2012  RRR  Creation                                  *
*                                                                            *
*****************************************************************************/


#if @HELP_CHEBWIN

    CHEBWIN

    Purpose: Multiplies a series with a Dolph-Chebyshev window.

    Syntax:  CHEBWIN(s, ampflag, attn)

                     s - A series, the input series.

               ampflag - Optional, an integer, the correction factor.

                          0: do not correct amplitude (default)
                          1: correct amplitude
                          2: correct RMS 
                          3: correct mean squared amplitude

                  attn - Optional. A real, the sidelobe attenuation
                         in dB from the mainlobe. Defaults to -100.

    Returns: A series.

    Example:
             W1: gsin(1000, 0.001, 45)
             W2: chebwin(w1)

             W1 contains a 1000 point sinewave with a frequency of 45 Hz.
             W2 multiplies the sinewave with a Dolph-Chebyshev window.

    Example:
             W1: gsin(1000, 0.001, 45)
             W2: chebwin(w1, 0, -65)

             Same as the first example except the sidelobe attenuation
             is -65 dB.

    Example:
             W1: chebwin(100, 0, -60)
             W2: magspec(w1, 8192);20*log10(curr/max(curr));

             W1 Creates a 100 point Dolph-Chebyshev window where the
             sidelobe attenuation is -60 dB. W2 displays the normalized
             frequency response.

    Remarks:
             The frequency response of an Nth order Dolph-Chebyshev
             window with an attenuation of attn decibels is given by:

             W(k) = Cheb(N-1, beta * cos(pi * k / (N-1))) / Cheb(N-1, beta)

             where:

             Cheb(m, x) is the mth order Chebyshev polynomial and

             beta = cosh(acosh(10 ^ (attn / 20)) / (N-1))

             The time domain response is determined by computing the 
             inverse Fourier transform and scaling the result to a
             unitary maximum.

             The Dolph-Chebyshev windows minimizes the Chebyshev norm of
             the sidelobes for a given mainlobe width.

             The Dolph-Chebyshev window can be regarded as the impulse
             response of an optimal Chebyshev lowpass filter having a
             zero-width passband.

             Because the Dolph-Chebyshev window yields equiripple constant
             magnitude sidelobes, impulses may result at the end points of
             the time domain response.

             Use GCHEBWIN to generate an N point Dolph-Chebyshev window.

               gchebwin(100, 1/100, -60)

             creates a 100 point Dolph-Chebyshev window with a sample rate
             of 0.01 and an attenuation of -60 dB.

    See Also:
             FFT
             GHAMMIMG
             GHANNING
             GKAISER
             GCHEBWIN
             GTAYLORWIN
             PSD
             SPECTRUM
#endif


/* multiply a series with a Dolph-Chebyshev window */
SERIES ITERATE chebwin(s, ampflag, attn)
{
        if (argc < 3)
        {
                if (argc < 2)
                {
                        if (argc < 1) error("chebwin - input required");

                        ampflag = 0;
                }

                attn = -100;
        }

        return(winfunc(7, s, ampflag, attn));
}