add numerical recipes library

lib/nr/ansi/examples/xeulsum.c

@@ -0,0 +1,41 @@
+
+/* Driver for routine eulsum */
+
+#include <stdio.h>
+#include <math.h>
+#define NRANSI
+#include "nr.h"
+#include "nrutil.h"
+
+#define NVAL 40
+
+int main(void)
+{
+	int i,j,mval;
+	float sum,term,x,xpower,*wksp;
+
+	wksp=vector(1,NVAL);
+	/* evaluate ln(1+x)=x-x^2/2+x^3/3-x^4/4 ... for -1<x<1 */
+	for (;;) {
+		printf("\nHow many terms in polynomial?\n");
+		printf("Enter n between 1 and %2d. (n=0 to end) ",NVAL);
+		scanf("%d",&mval);
+		printf("\n");
+		if ((mval <= 0) || (mval > NVAL)) break;
+		printf("%9s %14s %14s\n","x","actual","polynomial");
+		for (i = -8;i<=8;i++) {
+			x=i/10.0;
+			sum=0.0;
+			xpower = -1;
+			for (j=1;j<=mval;j++) {
+				xpower *= (-x);
+				term=xpower/j;
+				eulsum(&sum,term,j,wksp);
+			}
+			printf("%12.6f %12.6f %12.6f\n",x,log(1.0+x),sum);
+		}
+	}
+	free_vector(wksp,1,NVAL);
+	return 0;
+}
+#undef NRANSI