code: def plotCastro(castroData, ylims, nstep=25, zlims=None):
      
      xlabel = "Energy [MeV]"
      ylabel = NORM_LABEL[castroData.norm_type]
      return plotCastro_base(castroData, ylims,
                             xlabel, ylabel, nstep, zlims)
docs: Make a color plot (castro plot) of the 
          delta log-likelihood as a function of 
          energy and flux normalization
  
      castroData : A CastroData object, with the 
                   log-likelihood v. normalization for each energy bin
      ylims      : y-axis limits
      nstep      : Number of y-axis steps to plot for each energy bin
      zlims      : z-axis limits
  
      returns fig,ax,im,ztmp which are matplotlib figure, axes and image objects