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 forcedens(title, pos, fdens, ax=0):
    """plot force densities"""
    if ax == 0:
        ax = plt.gca()
    ax.set_title(title)
    ax.grid(True)

    ax.plot(pos, [1e-3*ft for ft in fdens[0]], label='F tang')
    ax.plot(pos, [1e-3*fn for fn in fdens[1]], label='F norm')
    ax.legend()
    ax.set_xlabel('Pos / deg')
    ax.set_ylabel('Force Density / kN/m²')