add numerical recipes library

lib/nr/ansi/recipes/splint.c

@@ -0,0 +1,20 @@
+
+void splint(float xa[], float ya[], float y2a[], int n, float x, float *y)
+{
+	void nrerror(char error_text[]);
+	int klo,khi,k;
+	float h,b,a;
+
+	klo=1;
+	khi=n;
+	while (khi-klo > 1) {
+		k=(khi+klo) >> 1;
+		if (xa[k] > x) khi=k;
+		else klo=k;
+	}
+	h=xa[khi]-xa[klo];
+	if (h == 0.0) nrerror("Bad xa input to routine splint");
+	a=(xa[khi]-x)/h;
+	b=(x-xa[klo])/h;
+	*y=a*ya[klo]+b*ya[khi]+((a*a*a-a)*y2a[klo]+(b*b*b-b)*y2a[khi])*(h*h)/6.0;
+}