/* Demonstration of contour plotting */
      
#define NPTS      41

float tr[6] = {0.05, 0.0, -1.05, 0.0, 0.05, -1.05};

static float clevel[11] = {-1.,-.8,-.6,-.4,-.2,0,.2,.4,.6,.8,1.};

static int mark=1500, space=1500;

main()
{
      int i, j;
      float xx, yy;
      float z[NPTS][NPTS], w[NPTS][NPTS];
      void xform();

      for (i=0; i<NPTS; i++) {
        xx = (double)(i-(NPTS/2))/(double)(NPTS/2);
        for (j=0; j<NPTS; j++)  {
          yy = (double)(j-(NPTS/2))/(double)(NPTS/2) - 1.0;
          z[i][j] = xx*xx - yy*yy;
          w[i][j] = 2*xx*yy;
        }
      }

      plstar(1,1);
      plenv(-1.0,1.0,-1.0,1.0,0,0);
      plcont(z,NPTS,NPTS,1,NPTS,1,NPTS,clevel,11,xform);
      plstyl(1,&mark,&space);
      plcont(w,NPTS,NPTS,1,NPTS,1,NPTS,clevel,11,xform);
      pllab("X Coordinate", "Y Coordinate","Contour Plots of Saddle Points");
      pltext();
      plend();
}