#include <math.h>
#define NRANSI
#include "nrutil.h"
#define ITMAX 100
#define ZEPS 1.0e-10
#define MOV3(a,b,c, d,e,f) (a)=(d);(b)=(e);(c)=(f);

float dbrent(float ax, float bx, float cx, float (*f)(float),
	float (*df)(float), float tol, float *xmin)
{
	int iter,ok1,ok2;
	float a,b,d,d1,d2,du,dv,dw,dx,e=0.0;
	float fu,fv,fw,fx,olde,tol1,tol2,u,u1,u2,v,w,x,xm;

	a=(ax < cx ? ax : cx);
	b=(ax > cx ? ax : cx);
	x=w=v=bx;
	fw=fv=fx=(*f)(x);
	dw=dv=dx=(*df)(x);
	for (iter=1;iter<=ITMAX;iter++) {
		xm=0.5*(a+b);
		tol1=tol*fabs(x)+ZEPS;
		tol2=2.0*tol1;
		if (fabs(x-xm) <= (tol2-0.5*(b-a))) {
			*xmin=x;
			return fx;
		}
		if (fabs(e) > tol1) {
			d1=2.0*(b-a);
			d2=d1;
			if (dw != dx) d1=(w-x)*dx/(dx-dw);
			if (dv != dx) d2=(v-x)*dx/(dx-dv);
			u1=x+d1;
			u2=x+d2;
			ok1 = (a-u1)*(u1-b) > 0.0 && dx*d1 <= 0.0;
			ok2 = (a-u2)*(u2-b) > 0.0 && dx*d2 <= 0.0;
			olde=e;
			e=d;
			if (ok1 || ok2) {
				if (ok1 && ok2)
					d=(fabs(d1) < fabs(d2) ? d1 : d2);
				else if (ok1)
					d=d1;
				else
					d=d2;
				if (fabs(d) <= fabs(0.5*olde)) {
					u=x+d;
					if (u-a < tol2 || b-u < tol2)
						d=SIGN(tol1,xm-x);
				} else {
					d=0.5*(e=(dx >= 0.0 ? a-x : b-x));
				}
			} else {
				d=0.5*(e=(dx >= 0.0 ? a-x : b-x));
			}
		} else {
			d=0.5*(e=(dx >= 0.0 ? a-x : b-x));
		}
		if (fabs(d) >= tol1) {
			u=x+d;
			fu=(*f)(u);
		} else {
			u=x+SIGN(tol1,d);
			fu=(*f)(u);
			if (fu > fx) {
				*xmin=x;
				return fx;
			}
		}
		du=(*df)(u);
		if (fu <= fx) {
			if (u >= x) a=x; else b=x;
			MOV3(v,fv,dv, w,fw,dw)
			MOV3(w,fw,dw, x,fx,dx)
			MOV3(x,fx,dx, u,fu,du)
		} else {
			if (u < x) a=u; else b=u;
			if (fu <= fw || w == x) {
				MOV3(v,fv,dv, w,fw,dw)
				MOV3(w,fw,dw, u,fu,du)
			} else if (fu < fv || v == x || v == w) {
				MOV3(v,fv,dv, u,fu,du)
			}
		}
	}
	nrerror("Too many iterations in routine dbrent");
	return 0.0;
}
#undef ITMAX
#undef ZEPS
#undef MOV3
#undef NRANSI
/* (C) Copr. 1986-92 Numerical Recipes Software 9z!+!1(t+%. */