add numerical recipes library

lib/nr/k_and_r/recipes/rkdumb.c

@@ -0,0 +1,40 @@
+
+#include "nrutil.h"
+
+float **y,*xx;
+
+void rkdumb(vstart,nvar,x1,x2,nstep,derivs)
+float vstart[],x1,x2;
+int nstep,nvar;
+void (*derivs)();
+{
+	void rk4();
+	int i,k;
+	float x,h;
+	float *v,*vout,*dv;
+
+	v=vector(1,nvar);
+	vout=vector(1,nvar);
+	dv=vector(1,nvar);
+	for (i=1;i<=nvar;i++) {
+		v[i]=vstart[i];
+		y[i][1]=v[i];
+	}
+	xx[1]=x1;
+	x=x1;
+	h=(x2-x1)/nstep;
+	for (k=1;k<=nstep;k++) {
+		(*derivs)(x,v,dv);
+		rk4(v,dv,nvar,x,h,vout,derivs);
+		if ((float)(x+h) == x) nrerror("Step size too small in routine rkdumb");
+		x += h;
+		xx[k+1]=x;
+		for (i=1;i<=nvar;i++) {
+			v[i]=vout[i];
+			y[i][k+1]=v[i];
+		}
+	}
+	free_vector(dv,1,nvar);
+	free_vector(vout,1,nvar);
+	free_vector(v,1,nvar);
+}