add numerical recipes library

lib/nr/ansi/examples/xchebft.c

@@ -0,0 +1,50 @@
+
+/* Driver for routine chebft */
+
+#include <stdio.h>
+#include <math.h>
+#define NRANSI
+#include "nr.h"
+
+#define NVAL 40
+#define PIO2 1.5707963
+
+float func(float x)
+{
+	return x*x*(x*x-2.0)*sin(x);
+}
+
+int main(void)
+{
+	float a=(-PIO2),b=PIO2,dum,f;
+	float t0,t1,term,x,y,c[NVAL];
+	int i,j,mval;
+
+	chebft(a,b,c,NVAL,func);
+	/* test result */
+	for (;;) {
+		printf("\nHow many terms in Chebyshev evaluation?\n");
+		printf("Enter n between 6 and %2d. (n=0 to end).\n",NVAL);
+		scanf("%d",&mval);
+		if ((mval <= 0) || (mval > NVAL)) break;
+		printf("\n%9s %14s %16s\n","x","actual","chebyshev fit");
+		for (i = -8;i<=8;i++) {
+			x=i*PIO2/10.0;
+			y=(x-0.5*(b+a))/(0.5*(b-a));
+			/* Evaluate Chebyshev polynomial without CHEBEV */
+			t0=1.0;
+			t1=y;
+			f=c[1]*t1+c[0]*0.5;
+			for (j=2;j<mval;j++) {
+				dum=t1;
+				t1=2.0*y*t1-t0;
+				t0=dum;
+				term=c[j]*t1;
+				f += term;
+			}
+			printf("%12.6f %12.6f %12.6f\n",x,func(x),f);
+		}
+	}
+	return 0;
+}
+#undef NRANSI