def test_negative_scalar_index(adata, index: int, obs: bool):
    pos_index = index + (adata.n_obs if obs else adata.n_vars)

    if obs:
        adata_pos_subset = adata[pos_index]
        adata_neg_subset = adata[index]
    else:
        adata_pos_subset = adata[:, pos_index]
        adata_neg_subset = adata[:, index]

    np.testing.assert_array_equal(
        adata_pos_subset.obs_names, adata_neg_subset.obs_names
    )
    np.testing.assert_array_equal(
        adata_pos_subset.var_names, adata_neg_subset.var_names
    )
def mcv_muer(mcv, ax=0):
    """plot rel. permeability vs. B of mcv dict"""
    MUE0 = 4e-7*np.pi
    bi, ur = zip(*[(bx, bx/hx/MUE0)
                   for bx, hx in zip(mcv['curve'][0]['bi'],
                                     mcv['curve'][0]['hi']) if not hx == 0])
    if ax == 0:
        ax = plt.gca()
    ax.plot(bi, ur)
    ax.set_xlabel('B / T')
    ax.set_title('rel. Permeability')
    ax.grid()