add numerical recipes library

lib/nr/k_and_r/recipes/fgauss.c

@@ -0,0 +1,21 @@
+
+#include <math.h>
+
+void fgauss(x,a,y,dyda,na)
+float *y,a[],dyda[],x;
+int na;
+{
+	int i;
+	float fac,ex,arg;
+
+	*y=0.0;
+	for (i=1;i<=na-1;i+=3) {
+		arg=(x-a[i+1])/a[i+2];
+		ex=exp(-arg*arg);
+		fac=a[i]*ex*2.0*arg;
+		*y += a[i]*ex;
+		dyda[i]=ex;
+		dyda[i+1]=fac/a[i+2];
+		dyda[i+2]=fac*arg/a[i+2];
+	}
+}