Plots the costs of the given generators.

def plotGenCost(generators):
    """ Plots the costs of the given generators.
    """
    figure()
    plots = []
    for generator in generators:
        if generator.pcost_model == PW_LINEAR:
            x = [x for x, _ in generator.p_cost]
            y = [y for _, y in generator.p_cost]
        elif generator.pcost_model == POLYNOMIAL:
            x = scipy.arange(generator.p_min, generator.p_max, 5)
            y = scipy.polyval(scipy.array(generator.p_cost), x)
        else:
            raise
        plots.append(plot(x, y))
        xlabel("P (MW)")
        ylabel("Cost ($)")
    legend(plots, [g.name for g in generators])
    show()