From 679b12958dcab408a097a42d172a0b3368105b31 Mon Sep 17 00:00:00 2001
From: JoepVanlier <joep.vanlier@gmail.com>
Date: Tue, 26 Sep 2023 17:35:51 +0200
Subject: [PATCH] diffusion: better error for "ols" of empty track

---
 changelog.md                                        |  1 +
 lumicks/pylake/kymotracker/detail/msd_estimation.py |  6 ++++++
 lumicks/pylake/kymotracker/tests/test_kymotrack.py  | 12 ++++++++++++
 3 files changed, 19 insertions(+)

diff --git a/changelog.md b/changelog.md
index a960146f1..1c2ee59fe 100644
--- a/changelog.md
+++ b/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
 
diff --git a/lumicks/pylake/kymotracker/detail/msd_estimation.py b/lumicks/pylake/kymotracker/detail/msd_estimation.py
index cf7777ee4..370a63e8e 100644
--- a/lumicks/pylake/kymotracker/detail/msd_estimation.py
+++ b/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)
diff --git a/lumicks/pylake/kymotracker/tests/test_kymotrack.py b/lumicks/pylake/kymotracker/tests/test_kymotrack.py
index 94a0fad3a..e305f4ac4 100644
--- a/lumicks/pylake/kymotracker/tests/test_kymotrack.py
+++ b/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"""