Create a two-dimensional scatter plot.

    INPUTS

def twoDimensionalScatter(title, title_x, title_y,
                          x, y,
                          lim_x = None, lim_y = None,
                          color = 'b', size = 20, alpha=None):
    """
    Create a two-dimensional scatter plot.

    INPUTS
    """
    plt.figure()

    plt.scatter(x, y, c=color, s=size, alpha=alpha, edgecolors='none')
    
    plt.xlabel(title_x)
    plt.ylabel(title_y)
    plt.title(title)
    if type(color) is not str:
        plt.colorbar()

    if lim_x:
        plt.xlim(lim_x[0], lim_x[1])
    if lim_y:
        plt.ylim(lim_y[0], lim_y[1])