def plot_imag(fignum, Bimag, Mimag, s):
    """
    function to plot d (Delta M)/dB  curves
    """
    plt.figure(num=fignum)
    plt.clf()
    if not isServer:
        plt.figtext(.02, .01, version_num)
    plt.plot(Bimag, Mimag, 'r')
    plt.xlabel('B (T)')
    plt.ylabel('M/Ms')
    plt.axvline(0, color='k')
    plt.title(s)