PEAKS  A sample function of two variables.
    PEAKS is a function of two variables, obtained by translating and
    scaling Gaussian distributions, which is useful for demonstrating
    MESH, SURF, PCOLOR, CONTOUR, etc.
    There are several variants of the calling sequence:

        Z = PEAKS;
        Z = PEAKS(N);
        Z = PEAKS(V);
        Z = PEAKS(X,Y);

        PEAKS;
        PEAKS(N);
        PEAKS(V);
        PEAKS(X,Y);

        [X,Y,Z] = PEAKS;
        [X,Y,Z] = PEAKS(N);
        [X,Y,Z] = PEAKS(V);

    The first variant produces a 49-by-49 matrix.
    The second variant produces an N-by-N matrix.
    The third variant produces an N-by-N matrix where N = length(V).
    The fourth variant evaluates the function at the given X and Y,
    which must be the same size.  The resulting Z is also that size.

    The next four variants, with no output arguments, do a SURF
    plot of the result.

    The last three variants also produce two matrices, X and Y, for
    use in commands such as PCOLOR(X,Y,Z) or SURF(X,Y,Z,DEL2(Z)).

    If not given as input, the underlying matrices X and Y are
        [X,Y] = MESHGRID(V,V)
    where V is a given vector, or V is a vector of length N with
    elements equally spaced from -3 to 3.  If no input argument is
    given, the default N is 49.