Docs boolean frame masks

doc/source/AUTHORS

@@ -46,3 +46,5 @@ Chronological list of authors
   - Rubén Chaves
 2025
   - Yu-Yuan (Stuart) Yang
+2026
+  - Francesco Siciliani

doc/source/examples/analysis/custom_trajectory_analysis.ipynb

@@ -410,6 +410,38 @@
     "plt.xlabel('Frame')"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "You can also select frames by passing a mask to the `frames` argument of the `run()` method. The mask contains one boolean value per frame; only frames marked `True` are analysed. The mask can be a NumPy boolean array or a Python list of booleans.\n",
+    "\n",
+    "For example, the following mask selects every second frame:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "mask = np.zeros(len(u.trajectory), dtype=bool)\n",
+    "mask[::2] = True\n",
+    "\n",
+    "rog_masked = AnalysisFromFunction(\n",
+    "    radgyr, u.trajectory, protein, protein.masses,\n",
+    "    total_mass=np.sum(protein.masses),\n",
+    ")\n",
+    "rog_masked.run(frames=mask);"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "You can also pass an array of integers to `frames`; in that case, the array directly specifies the frame indices to analyse."
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},