matplot: pcolor on non-rectangular grid

2D pseudo color plot on non-rectangular grid (function pcolor)

Code:

var i,j,x=[],y=[],z=[], r, theta;

// generate some data to plot
for (i=0; i < 100; i++) {
  x[i] = [];
  y[i] = [];
  z[i] = [];

  for (j=0; j < 100; j++) {
    r = 20 + i;
    theta = 2*Math.PI * j/99;
    x[i][j] = r*Math.cos(theta);
    y[i][j] = r*Math.sin(theta);
    z[i][j] = Math.cos(2*theta);
  }
}

fig = new matplot.Figure("plot",700,500);
ax = fig.axes();
ax.pcolor(x,y,z);
ax.colorbar();
ax.DataAspectRatio([1,1,1]);
fig.draw();