Fixed frame-index selection in occupancy calculation.

src/mdevaluate/extra/free_energy_landscape.py

@@ -80,10 +80,7 @@ def occupation_matrix(
     bins = [x_bins, y_bins, z_bins]
     # Trajectory is split for parallel computing
     size = math.ceil(len(frame_indices) / nodes)
-    indices = [
-        np.arange(len(frame_indices))[i : i + size]
-        for i in range(0, len(frame_indices), size)
-    ]
+    indices = [frame_indices[i : i + size] for i in range(0, len(frame_indices), size)]
     pool = mp.Pool(nodes)
     results = pool.map(
         partial(_calc_histogram, trajectory=trajectory, bins=bins), indices