add numerical recipes library

lib/nr/ansi/recipes/zbrac.c

@@ -0,0 +1,25 @@
+
+#include <math.h>
+#define FACTOR 1.6
+#define NTRY 50
+
+int zbrac(float (*func)(float), float *x1, float *x2)
+{
+	void nrerror(char error_text[]);
+	int j;
+	float f1,f2;
+
+	if (*x1 == *x2) nrerror("Bad initial range in zbrac");
+	f1=(*func)(*x1);
+	f2=(*func)(*x2);
+	for (j=1;j<=NTRY;j++) {
+		if (f1*f2 < 0.0) return 1;
+		if (fabs(f1) < fabs(f2))
+			f1=(*func)(*x1 += FACTOR*(*x1-*x2));
+		else
+			f2=(*func)(*x2 += FACTOR*(*x2-*x1));
+	}
+	return 0;
+}
+#undef FACTOR
+#undef NTRY