def chart_plot(self, ax=None, cmap='<STR_LIT>',<EOL>xlabel='<STR_LIT:N>', ylabel='<STR_LIT>', grid_on=True, colorbar=True):
from matplotlib.mlab import griddata<EOL>from numpy import linspace, meshgrid<EOL>import matplotlib.pyplot as plt<EOL>x = self.dropna().N<EOL>y = self.dropna().Z<EOL>z = self.dropna().values<EOL>xi = linspace(min(x), max(x), max(x) - min(x) + <NUM_LIT:1>)<EOL>yi = linspace(min(y), max(y), max(y) - min(y) + <NUM_LIT:1>)<EOL>Z = griddata(x, y, z, xi, yi)<EOL>X, Y = meshgrid(xi, yi)<EOL>if ax is None:<EOL><INDENT>ax = plt.gca()<EOL><DEDENT>chart = ax.pcolormesh(X, Y, Z, cmap=cmap)<EOL>ax.set_xlabel(xlabel)<EOL>ax.set_ylabel(ylabel)<EOL>ax.grid(grid_on)<EOL>ax.set_aspect('<STR_LIT>')<EOL>if colorbar:<EOL><INDENT>plt.colorbar(chart)<EOL><DEDENT>return ax<EOL>
Plot a nuclear chart with (N,Z) as axis and the values
        of the Table as a color scale

        Parameters
        ----------
        ax: optional matplotlib axes
                defaults to current axes
        cmap: a matplotlib colormap
                default: 'RdBu'
        xlabel: string representing the label of the x axis
            default: 'N'
        ylabel: string, default: 'Z'
            the label of the x axis
        grid_on: boolean, default: True,
            whether to draw the axes grid or not
        colorbar: boolean, default: True
            whether to draw a colorbar or not

        Returns
        -------
        ax: a matplotlib axes object

        Example
        -------
        Plot the theoretical deviation for the Möller's model::

        >>> Table('FRDM95').error().chart_plot()