function drawX (x, y, color)
% Draw an X in square (x,y) using color.
% Parameter color is a single character; same color-scheme as plot().
% Parameters x and y are integers; (x,y) is lower left corner of square
% (x,y).

xcen = x + 0.5;
ycen = y + 0.5;
plot([xcen - 0.25, xcen + 0.25], [ycen + 0.25, ycen - 0.25], color);
plot([xcen - 0.25, xcen + 0.25], [ycen - 0.25, ycen + 0.25], color);
