add numerical recipes library

lib/nr/ansi/recipes/rtflsp.c

@@ -0,0 +1,43 @@
+
+#include <math.h>
+#define MAXIT 30
+
+float rtflsp(float (*func)(float), float x1, float x2, float xacc)
+{
+	void nrerror(char error_text[]);
+	int j;
+	float fl,fh,xl,xh,swap,dx,del,f,rtf;
+
+	fl=(*func)(x1);
+	fh=(*func)(x2);
+	if (fl*fh > 0.0) nrerror("Root must be bracketed in rtflsp");
+	if (fl < 0.0) {
+		xl=x1;
+		xh=x2;
+	} else {
+		xl=x2;
+		xh=x1;
+		swap=fl;
+		fl=fh;
+		fh=swap;
+	}
+	dx=xh-xl;
+	for (j=1;j<=MAXIT;j++) {
+		rtf=xl+dx*fl/(fl-fh);
+		f=(*func)(rtf);
+		if (f < 0.0) {
+			del=xl-rtf;
+			xl=rtf;
+			fl=f;
+		} else {
+			del=xh-rtf;
+			xh=rtf;
+			fh=f;
+		}
+		dx=xh-xl;
+		if (fabs(del) < xacc || f == 0.0) return rtf;
+	}
+	nrerror("Maximum number of iterations exceeded in rtflsp");
+	return 0.0;
+}
+#undef MAXIT