add numerical recipes library

lib/nr/k_and_r/recipes/midexp.c

@@ -0,0 +1,34 @@
+
+#include <math.h>
+#define FUNC(x) ((*funk)(-log(x))/(x))
+
+float midexp(funk,aa,bb,n)
+float (*funk)(),aa,bb;
+int n;
+{
+	float x,tnm,sum,del,ddel,a,b;
+	static float s;
+	int it,j;
+
+	b=exp(-aa);
+	a=0.0;
+	if (n == 1) {
+		return (s=(b-a)*FUNC(0.5*(a+b)));
+	} else {
+		for(it=1,j=1;j<n-1;j++) it *= 3;
+		tnm=it;
+		del=(b-a)/(3.0*tnm);
+		ddel=del+del;
+		x=a+0.5*del;
+		sum=0.0;
+		for (j=1;j<=it;j++) {
+			sum += FUNC(x);
+			x += ddel;
+			sum += FUNC(x);
+			x += del;
+		}
+		s=(s+(b-a)*sum/tnm)/3.0;
+		return s;
+	}
+}
+#undef FUNC