error ellipse, "ellipse walls" version
/// ERROR_ELLIPSE(C22) - Given a 2x2 covariance matrix, plot the
/// associated error ellipse, at the origin. It returns a graphics handle
/// of the ellipse that was drawn.
///
/// ERROR_ELLIPSE(C33) - Given a 3x3 covariance matrix, plot the
/// associated error ellipsoid, at the origin, as well as its projections
/// onto the three axes. Returns a vector of 4 graphics handles, for the
/// three ellipses (in the X-Y, Y-Z, and Z-X planes, respectively) and for
/// the ellipsoid.
///
/// ERROR_ELLIPSE(C,MU) - Plot the ellipse, or ellipsoid, centered at MU,
/// a vector whose length should match that of C (which is 2x2 or 3x3).
///
/// ERROR_ELLIPSE(...,'Property1',Value1,'Name2',Value2,...) sets the
/// values of specified properties, including:
/// 'C' - Alternate method of specifying the covariance matrix
/// 'mu' - Alternate method of specifying the ellipse (-oid) center
/// 'conf' - A value betwen 0 and 1 specifying the confidence interval.
/// the default is 0.5 which is the 50%> error ellipse.
/// 'scale' - Allow the plot the be scaled to difference units.
/// 'style' - A plotting style used to format ellipses.
/// 'clip' - specifies a clipping ruleRadii. Portions of the ellipse, -oid,
/// outside the ruleRadii will not be shown.
///
/// NOTES: C must be positive definite for this function to work properly.
///
Definition in file error_ellipse2.m.