SURF   3-D colored surface.
    SURF(X,Y,Z,C) plots the colored parametric surface defined by
    four matrix arguments.  The view point is specified by VIEW.
    The axis labels are determined by the range of X, Y and Z,
    or by the current setting of AXIS.  The color scaling is determined
    by the range of C, or by the current setting of CAXIS.  The scaled
    color values are used as indices into the current COLORMAP.
    The shading model is set by SHADING.