diffusion: better error for "ols" of empty track

changelog.md

@@ -11,6 +11,7 @@
 #### Improvements
 
 * Kymographs that only consist of a single line no longer raise, but report a `line_time_seconds`. This also allows you to now call `Kymo.plot()` on these.
+* Issue a more descriptive error when attempting to compute a diffusion constant of a track with no points.
 
 ## v1.2.1 | 2023-10-17
 

lumicks/pylake/kymotracker/detail/msd_estimation.py

@@ -735,6 +735,12 @@ def determine_optimal_points(frame_idx, coordinate, max_iterations=100):
 
         num_slopes.add(num_slope)
 
+        if len(coordinate) <= 4:
+            raise RuntimeError(
+                "You need at least 5 time points to estimate the number of points to include in "
+                "the fit."
+            )
+
         # Determine the number of points to include in the next fit
         num_slope, num_intercept = optimal_points(
             calculate_localization_error(frame_lags[:num_slope], msd[:num_slope]), len(coordinate)

lumicks/pylake/kymotracker/tests/test_kymotrack.py

@@ -1211,6 +1211,18 @@ def make_coordinates(length, divisor):
         d = tracks.estimate_diffusion("ols", min_length=2)
 
 
+@pytest.mark.parametrize("data", [[], [1, 2, 3, 4]])
+def test_ols_empty_kymotrack(blank_kymo, data):
+    track = KymoTrack(data, data, blank_kymo, "red", 0)
+
+    with pytest.raises(
+        RuntimeError,
+        match="You need at least 5 time points to estimate the number of points to include in the "
+        "fit.",
+    ):
+        track.estimate_diffusion("ols")
+
+
 @pytest.mark.parametrize("kbp_calibration, line_width", [(None, 7), (4, 7), (None, 8)])
 def test_ensemble_msd_calibration_from_kymo(blank_kymo, kbp_calibration, line_width):
     """Checks whether all the properties are correctly forwarded from the Kymo"""