add numerical recipes library

lib/nr/ansi/recipes/trapzd.c

@@ -0,0 +1,22 @@
+
+#define FUNC(x) ((*func)(x))
+
+float trapzd(float (*func)(float), float a, float b, int n)
+{
+	float x,tnm,sum,del;
+	static float s;
+	int it,j;
+
+	if (n == 1) {
+		return (s=0.5*(b-a)*(FUNC(a)+FUNC(b)));
+	} else {
+		for (it=1,j=1;j<n-1;j++) it <<= 1;
+		tnm=it;
+		del=(b-a)/tnm;
+		x=a+0.5*del;
+		for (sum=0.0,j=1;j<=it;j++,x+=del) sum += FUNC(x);
+		s=0.5*(s+(b-a)*sum/tnm);
+		return s;
+	}
+}
+#undef FUNC