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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def expand_rmf_matrix(rmf):
 """Expand an RMF matrix stored in compressed form. *rmf* An RMF object as might be returned by ``sherpa.astro.ui.get_rmf()``. Returns: A non-sparse RMF matrix. The Response Matrix Function (RMF) of an X-ray telescope like Chandra can be stored in a sparse format as defined in `OGIP Calibration Memo CAL/GEN/92-002 <https://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/memos/cal_gen_92_002/cal_gen_92_002.html>`_. For visualization and analysis purposes, it can be useful to de-sparsify the matrices stored in this way. This function does that, returning a two-dimensional Numpy array. """

    n_chan = rmf.e_min.size
    n_energy = rmf.n_grp.size

    expanded = np.zeros((n_energy, n_chan))
    mtx_ofs = 0
    grp_ofs = 0

    for i in range(n_energy):
        for j in range(rmf.n_grp[i]):
            f = rmf.f_chan[grp_ofs]
            n = rmf.n_chan[grp_ofs]
            expanded[i,f:f+n] = rmf.matrix[mtx_ofs:mtx_ofs+n]
            mtx_ofs += n
            grp_ofs += 1

    return expanded