Hi there,
Depending on what type of matrix chart you're making, it should be fairly simple to do in OmniGraphSketcher for iPad. You can either choose to center the axes on the canvas and make the four quadrants the boxes of the matrix, or leave the origin in the bottom left and draw the quadrants with lines or fills. Use the info popover to hide the axis ticks and tick labels, and you should be good to go!
Let us know if you have any questions, either here or by emailing
OmniGraphSketcher-iPad@omnigroup.com