add numerical recipes library

lib/nr/ansi/recipes/zriddr.c

@@ -0,0 +1,54 @@
+
+#include <math.h>
+#define NRANSI
+#include "nrutil.h"
+#define MAXIT 60
+#define UNUSED (-1.11e30)
+
+float zriddr(float (*func)(float), float x1, float x2, float xacc)
+{
+	int j;
+	float ans,fh,fl,fm,fnew,s,xh,xl,xm,xnew;
+
+	fl=(*func)(x1);
+	fh=(*func)(x2);
+	if ((fl > 0.0 && fh < 0.0) || (fl < 0.0 && fh > 0.0)) {
+		xl=x1;
+		xh=x2;
+		ans=UNUSED;
+		for (j=1;j<=MAXIT;j++) {
+			xm=0.5*(xl+xh);
+			fm=(*func)(xm);
+			s=sqrt(fm*fm-fl*fh);
+			if (s == 0.0) return ans;
+			xnew=xm+(xm-xl)*((fl >= fh ? 1.0 : -1.0)*fm/s);
+			if (fabs(xnew-ans) <= xacc) return ans;
+			ans=xnew;
+			fnew=(*func)(ans);
+			if (fnew == 0.0) return ans;
+			if (SIGN(fm,fnew) != fm) {
+				xl=xm;
+				fl=fm;
+				xh=ans;
+				fh=fnew;
+			} else if (SIGN(fl,fnew) != fl) {
+				xh=ans;
+				fh=fnew;
+			} else if (SIGN(fh,fnew) != fh) {
+				xl=ans;
+				fl=fnew;
+			} else nrerror("never get here.");
+			if (fabs(xh-xl) <= xacc) return ans;
+		}
+		nrerror("zriddr exceed maximum iterations");
+	}
+	else {
+		if (fl == 0.0) return x1;
+		if (fh == 0.0) return x2;
+		nrerror("root must be bracketed in zriddr.");
+	}
+	return 0.0;
+}
+#undef MAXIT
+#undef UNUSED
+#undef NRANSI