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/* Written by Charles Harris charles.harris@sdl.usu.edu */
#include "zeros.h"
double
bisect(callback_type f, double xa, double xb, double xtol, double rtol, int iter, default_parameters *params)
{
int i;
double dm,xm,fm,fa,fb,tol;
tol = xtol + rtol*(fabs(xa) + fabs(xb));
fa = (*f)(xa,params);
fb = (*f)(xb,params);
params->funcalls = 2;
if (fa*fb > 0) {ERROR(params,SIGNERR,0.0);}
if (fa == 0) return xa;
if (fb == 0) return xb;
dm = xb - xa;
params->iterations = 0;
for(i=0; i<iter; i++) {
params->iterations++;
dm *= .5;
xm = xa + dm;
fm = (*f)(xm,params);
params->funcalls++;
if (fm*fa >= 0) {
xa = xm;
}
if (fm == 0 || fabs(dm) < tol)
return xm;
}
ERROR(params,CONVERR,xa);
}
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