PCOLOR plot with XMID and YMID marking the
    *centers* of the cells of Z.  X and Y need to be monotonic, but do not 
    need to have uniform spacing.
 
    This is unlike PCOLOR(X,Y,Z), where X and Y mark the cell *edges*.  
 
    Similarly, unlike PCOLOR, <a href="jpcolor.html">JPCOLOR</a> does not throw away the last row and
    column of Z. It also specifies the axes to be centered on the cells.
 
    <a href="jpcolor.html">JPCOLOR</a> also automatically applies SQUEEZE to Z, which is useful for 
    