add numerical recipes library

lib/nr/ansi/examples/xmglin.c

@@ -0,0 +1,43 @@
+
+/* Driver for routine mglin */
+
+#include <stdio.h>
+#include <math.h>
+#define NRANSI
+#include "nr.h"
+#include "nrutil.h"
+
+#define NSTEP 4
+#define JMAX 33
+
+int main(void)
+{
+	int i,j,midl=JMAX/2+1;
+	double **f,**u;
+
+	f=dmatrix(1,JMAX,1,JMAX);
+	u=dmatrix(1,JMAX,1,JMAX);
+	for (i=1;i<=JMAX;i++)
+		for (j=1;j<=JMAX;j++)
+			u[i][j]=0.0;
+	u[midl][midl]=2.0;
+	mglin(u,JMAX,2);
+	printf("MGLIN solution:\n");
+	for (i=1;i<=JMAX;i+=NSTEP) {
+		for (j=1;j<=JMAX;j+=NSTEP) printf("%8.4f",u[i][j]);
+		printf("\n");
+	}
+	printf("\n Test that solution satisfies difference equations:\n");
+	for (i=NSTEP+1;i<JMAX;i+=NSTEP) {
+		for (j=NSTEP+1;j<JMAX;j+=NSTEP)
+			f[i][j]=u[i+1][j]+u[i-1][j]+u[i][j+1]+u[i][j-1]
+				-4.0*u[i][j];
+		printf("%7s"," ");
+		for (j=NSTEP+1;j<JMAX;j+=NSTEP) printf("%8.4f",f[i][j]*(JMAX-1)*(JMAX-1));
+		printf("\n");
+	}
+	free_dmatrix(u,1,JMAX,1,JMAX);
+	free_dmatrix(f,1,JMAX,1,JMAX);
+	return 0;
+}
+#undef NRANSI