zero_t.c
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	#include<stdio.h>
	#include<math.h>
	#include<fonction.h>
	#include<constant.h>
	#include<dimension.h>
	#include<structure.h>

	/****************************************************************/
	/* nom: zero (methode des tangentes) */
	/* auteur: Jean-Paul Kneib */
	/* date: 10/11/93 */
	/* place: Toulouse */
	/****************************************************************
	* Global variables used :
	* - none
	*/
	double zero_t(double c1, double c2, double (*f)(double))
	{
	double dc, c, fc, c0, fc0, tang, errc = .005;
	double fc1, fc2;
	int end = 0, nb = 0;

	fc1 = (*f)(c1);
	fc2 = (*f)(c2);
	if (fabs(fc1) < fabs(fc2))
	{
	c = c2;
	c2 = c1;
	c1 = c;
	fc = fc2;
	fc2 = fc1;
	fc1 = fc;
	};

	do
	{
	nb++;
	tang = (c2 - c1) / (fc2 - fc1);
	c0 = c2 - fc2 * tang;

	if (c0 > 1.)
	{
	end = 1;
	c1 = c2 = 0.8;
	}
	else if (c0 < 0.)
	{
	end = 1;
	c1 = c2 = 0.;
	}
	else
	{
	fc0 = (*f)(c0);

	if ((fc0*fc2) < 0)
	{
	c1 = c0;
	fc1 = fc0;
	}
	else if (fabs(fc0) < fabs(fc2))
	{
	c1 = c2;
	fc1 = fc2;
	c2 = c0;
	fc2 = fc0;
	}
	else
	end = 1;
	};

	dc = fabs(c1 - c2);

	}
	while ((end == 0) && (dc > errc) && (nb < 50));

	return ((c1 + c2) / 2.);
	}