add numerical recipes library

lib/nr/cpp/recipes/rkdumb.cpp

@@ -0,0 +1,36 @@
+#include "nr.h"
+
+extern Vec_DP *xx_p;
+extern Mat_DP *y_p;
+
+void NR::rkdumb(Vec_I_DP &vstart, const DP x1, const DP x2,
+	void derivs(const DP, Vec_I_DP &, Vec_O_DP &))
+{
+	int i,k;
+	DP x,h;
+
+	Vec_DP &xx=*xx_p;
+	Mat_DP &y=*y_p;
+	int nvar=y.nrows();
+	int nstep=y.ncols()-1;
+	Vec_DP v(nvar),vout(nvar),dv(nvar);
+	for (i=0;i<nvar;i++) {
+		v[i]=vstart[i];
+		y[i][0]=v[i];
+	}
+	xx[0]=x1;
+	x=x1;
+	h=(x2-x1)/nstep;
+	for (k=0;k<nstep;k++) {
+		derivs(x,v,dv);
+		rk4(v,dv,x,h,vout,derivs);
+		if (x+h == x)
+			nrerror("Step size too small in routine rkdumb");
+		x += h;
+		xx[k+1]=x;
+		for (i=0;i<nvar;i++) {
+			v[i]=vout[i];
+			y[i][k+1]=v[i];
+		}
+	}
+}