<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def plot_projected_dos(self, pdos_indices=None, legend=None):
 """Plot projected DOS Parameters pdos_indices : list of list, optional Sets of indices of atoms whose projected DOS are summed over. The indices start with 0. An example is as follwos: pdos_indices=[[0, 1], [2, 3, 4, 5]] Default is None, which means pdos_indices=[[i] for i in range(natom)] legend : list of instances such as str or int, optional The str(instance) are shown in legend. It has to be len(pdos_indices)==len(legend). Default is None. When None, legend is not shown. """


        import matplotlib.pyplot as plt

        fig, ax = plt.subplots()
        ax.xaxis.set_ticks_position('both')
        ax.yaxis.set_ticks_position('both')
        ax.xaxis.set_tick_params(which='both', direction='in')
        ax.yaxis.set_tick_params(which='both', direction='in')

        self._pdos.plot(ax,
                        indices=pdos_indices,
                        legend=legend,
                        draw_grid=False)

        ax.set_ylim((0, None))

        return plt