dspl/butter__ap__zp_8c_source.html

/*

* Copyright (c) 2015-2022 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 <stdio.h>

#include <stdlib.h>

#include <string.h>

#include "dspl.h"


#ifdef DOXYGEN_ENGLISH


#endif

#ifdef DOXYGEN_RUSSIAN


#endif

int DSPL_API butter_ap_zp(int ord, double rp, complex_t* z, int* nz,

                          complex_t *p, int* np)

{

    double alpha;

    double theta;

    double ep;

    int r;

    int L;

    int ind = 0, k;


    if(rp < 0 || rp == 0)

        return ERROR_FILTER_RP;

    if(ord < 1)

        return ERROR_FILTER_ORD;

    if(!z || !p || !nz || !np)

        return ERROR_PTR;


    ep = sqrt(pow(10.0, rp*0.1) - 1.0);

    r = ord % 2;

    L = (int)((ord-r)/2);


    alpha = pow(ep, -1.0/(double)ord);

    if(r)

    {

        RE(p[ind]) = -alpha;

        IM(p[ind]) = 0.0;

        ind++;

    }

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

    {

        theta = M_PI*(double)(2*k + 1)/(double)(2*ord);

        RE(p[ind]) = RE(p[ind+1]) = -alpha *    sin(theta);

        IM(p[ind]) =     alpha *    cos(theta);

        IM(p[ind+1]) =    -alpha *    cos(theta);

        ind+=2;

    }

    *np = ord;

    *nz = 0;

    return RES_OK;

}