dspl/fourier__series__dec_8c_source.html

/*

* Copyright (c) 2015-2024 Sergey Bakhurin

* Digital Signal Processing Library [http://dsplib.org]

*

* This file is part of libdspl-2.0.

*

* is free software: you can redistribute it and/or modify

* it under the terms of the GNU Lesser    General Public License as published by

* the Free Software Foundation, either version 3 of the License, or

* (at your option) any later version.

*

* DSPL is distributed in the hope that it will be useful,

* but WITHOUT ANY WARRANTY; without even the implied warranty of

* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.    See the

* GNU General Public License for more details.

*

* You should have received a copy of the GNU Lesser General Public License

* along with Foobar.    If not, see <http://www.gnu.org/licenses/>.

*/


#include <stdlib.h>

#include <string.h>

#include <math.h>

#include "dspl.h"


#ifdef DOXYGEN_ENGLISH


#endif

#ifdef DOXYGEN_RUSSIAN


#endif

int DSPL_API fourier_series_dec(double* t, double* s, int nt, double period,

                                                                int nw, double* w, complex_t* y)

{

    int k, m;

    double dw = M_2PI / period;

    complex_t e[2];


    if(!t || !s || !w || !y)

        return ERROR_PTR;

    if(nt<1 || nw < 1)

        return ERROR_SIZE;

    if(period <= 0.0)

        return ERROR_NEGATIVE;


    memset(y, 0 , nw*sizeof(complex_t));


    for(k = 0; k < nw; k++)

    {

        w[k] = (k - nw/2) * dw;

        RE(e[1]) =    s[0] * cos(w[k] * t[0]);

        IM(e[1]) = -s[0] * sin(w[k] * t[0]);

        for(m = 1; m < nt; m++)

        {

            RE(e[0]) = RE(e[1]);

            IM(e[0]) = IM(e[1]);

            RE(e[1]) =     s[m] * cos(w[k] * t[m]);

            IM(e[1]) = - s[m] * sin(w[k] * t[m]);

            RE(y[k]) += 0.5 * (RE(e[0]) + RE(e[1]))*(t[m] - t[m-1]);

            IM(y[k]) += 0.5 * (IM(e[0]) + IM(e[1]))*(t[m] - t[m-1]);

        }

        RE(y[k]) /= period;

        IM(y[k]) /= period;

    }


    if(!(nw%2))

        RE(y[0]) = RE(y[1]) = 0.0;


    return RES_OK;

}