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/* Written by Charles Harris charles.harris@sdl.usu.edu */
#include <math.h>
#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;
fa = (*f)(xa,params);
fb = (*f)(xb,params);
params->funcalls = 2;
if (fa*fb > 0) {
params->error_num = SIGNERR;
return 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) < xtol + rtol*fabs(xm)) {
return xm;
}
}
params->error_num = CONVERR;
return xa;
}
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