Internal helper function for making plots, returns a set of input values to plot as well as lower and upper limits

def x_frame2D(X,plot_limits=None,resolution=None):
    """
    Internal helper function for making plots, returns a set of input values to plot as well as lower and upper limits
    """
    assert X.shape[1] ==2, "x_frame2D is defined for two-dimensional inputs"
    if plot_limits is None:
        xmin,xmax = X.min(0),X.max(0)
        xmin, xmax = xmin-0.2*(xmax-xmin), xmax+0.2*(xmax-xmin)
    elif len(plot_limits)==2:
        xmin, xmax = plot_limits
    else:
        raise ValueError("Bad limits for plotting")

    resolution = resolution or 50
    xx,yy = np.mgrid[xmin[0]:xmax[0]:1j*resolution,xmin[1]:xmax[1]:1j*resolution]
    Xnew = np.vstack((xx.flatten(),yy.flatten())).T
    return Xnew, xx, yy, xmin, xmax