zero_premier.C

/*
 *  Locates the first zero of a function in a given interval.
 *
 */

/*
 *   Copyright (c) 1999-2001 Eric Gourgoulhon
 *
 *   This file is part of LORENE.
 *
 *   LORENE is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   LORENE 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 General Public License
 *   along with LORENE; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */


char zero_premier_C[] = "$Header: /cvsroot/Lorene/C++/Source/Non_class_members/Utilities/zero_premier.C,v 1.2 2002/10/16 14:37:12 j_novak Exp $" ;

/*
 * $Id: zero_premier.C,v 1.2 2002/10/16 14:37:12 j_novak Exp $
 * $Log: zero_premier.C,v $
 * Revision 1.2  2002/10/16 14:37:12  j_novak
 * Reorganization of #include instructions of standard C++, in order to
 * use experimental version 3 of gcc.
 *
 * Revision 1.1.1.1  2001/11/20 15:19:29  e_gourgoulhon
 * LORENE
 *
 * Revision 1.2  2000/01/04  10:57:51  eric
 * Le test f1*f2 < 0. est remplace par f1*f2 <= double(0).
 *
 * Revision 1.1  1999/12/24  13:00:10  eric
 * Initial revision
 *
 *
 * $Header: /cvsroot/Lorene/C++/Source/Non_class_members/Utilities/zero_premier.C,v 1.2 2002/10/16 14:37:12 j_novak Exp $
 *
 */

// Headers Lorene 
#include "headcpp.h"
#include "param.h"
//****************************************************************************

bool zero_premier(double (*f)(double, const Param&), const Param& par,
          double a, double b, int n, double& a0, double& b0) {

    double dx = (b-a)/double(n) ;     

    a0 = a ; 
    b0 = a0 + dx ; 

    double f1 = f(a0, par) ;
    bool trouve = false ; 
    
    for (int i=0; i<n; i++) {
    double f2 = f(b0, par) ;
    if (f1*f2 <= double(0)) {       // on a encadre le zero
        trouve = true ; 
        break ; 
    } 

    // On passe au sous-intervalle suivant :
    a0 = b0 ; 
    f1 = f2 ;  
    b0 += dx ;
    } 
    
    return trouve ; 

}

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