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76 lines
1.3 KiB
C
76 lines
1.3 KiB
C
#include <math.h>
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#include "header.h"
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#define ITMAX 100
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#define EPS 3.0e-8
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double zbrent(double (*func)(double), double x1,double x2, double tol)
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{
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int iter;
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double a=x1,b=x2,c,d,e,min1,min2;
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double fa=(*func)(a),fb=(*func)(b),fc,p,q,r,s,tol1,xm;
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void nrerror();
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if (fb*fa > 0.0)
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{
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printf("ERROR: Root must be bracketed in ZBRENT\n");
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ERROR_FLAG=1;
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return (x1+x2)/2;
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}
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fc=fb;
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for (iter=1;iter<=ITMAX;iter++) {
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if (fb*fc > 0.0) {
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c=a;
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fc=fa;
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e=d=b-a;
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}
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if (fabs(fc) < fabs(fb)) {
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a=b;
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b=c;
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c=a;
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fa=fb;
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fb=fc;
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fc=fa;
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}
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tol1=2.0*EPS*fabs(b)+0.5*tol;
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xm=0.5*(c-b);
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if (fabs(xm) <= tol1 || fb == 0.0) return b;
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if (fabs(e) >= tol1 && fabs(fa) > fabs(fb)) {
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s=fb/fa;
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if (a == c) {
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p=2.0*xm*s;
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q=1.0-s;
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} else {
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q=fa/fc;
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r=fb/fc;
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p=s*(2.0*xm*q*(q-r)-(b-a)*(r-1.0));
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q=(q-1.0)*(r-1.0)*(s-1.0);
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}
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if (p > 0.0) q = -q;
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p=fabs(p);
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min1=3.0*xm*q-fabs(tol1*q);
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min2=fabs(e*q);
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if (2.0*p < (min1 < min2 ? min1 : min2)) {
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e=d;
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d=p/q;
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} else {
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d=xm;
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e=d;
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}
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} else {
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d=xm;
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e=d;
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}
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a=b;
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fa=fb;
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if (fabs(d) > tol1)
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b += d;
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else
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b += (xm > 0.0 ? fabs(tol1) : -fabs(tol1));
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fb=(*func)(b);
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}
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nrerror("Maximum number of iterations exceeded in ZBRENT");
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return(0);
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}
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#undef ITMAX
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#undef EPS
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