add numerical recipes library

lib/nr/k_and_r/recipes/rc.c

@@ -0,0 +1,53 @@
+
+#include <math.h>
+#include "nrutil.h"
+#define ERRTOL 0.04
+#define TINY 1.69e-38
+#define SQRTNY 1.3e-19
+#define BIG 3.e37
+#define TNBG (TINY*BIG)
+#define COMP1 (2.236/SQRTNY)
+#define COMP2 (TNBG*TNBG/25.0)
+#define THIRD (1.0/3.0)
+#define C1 0.3
+#define C2 (1.0/7.0)
+#define C3 0.375
+#define C4 (9.0/22.0)
+
+float rc(x,y)
+float x,y;
+{
+	float alamb,ave,s,w,xt,yt;
+	if (x < 0.0 || y == 0.0 || (x+fabs(y)) < TINY || (x+fabs(y)) > BIG ||
+		(y<-COMP1 && x > 0.0 && x < COMP2))
+			nrerror("invalid arguments in rc");
+	if (y > 0.0) {
+		xt=x;
+		yt=y;
+		w=1.0;
+	} else {
+		xt=x-y;
+		yt = -y;
+		w=sqrt(x)/sqrt(xt);
+	}
+	do {
+		alamb=2.0*sqrt(xt)*sqrt(yt)+yt;
+		xt=0.25*(xt+alamb);
+		yt=0.25*(yt+alamb);
+		ave=THIRD*(xt+yt+yt);
+		s=(yt-ave)/ave;
+	} while (fabs(s) > ERRTOL);
+	return w*(1.0+s*s*(C1+s*(C2+s*(C3+s*C4))))/sqrt(ave);
+}
+#undef ERRTOL
+#undef TINY
+#undef SQRTNY
+#undef BIG
+#undef TNBG
+#undef COMP1
+#undef COMP2
+#undef THIRD
+#undef C1
+#undef C2
+#undef C3
+#undef C4