Fixing execute loop for irregular dt

and adding unit test

Author: erikvansebille

parcels/kernel.py

@@ -381,16 +381,16 @@ def evaluate_particle(self, p, endtime):
             pre_dt = p.dt
 
             sign_dt = np.sign(p.dt).astype(int)
-            if sign_dt * (p.time_nextloop - endtime) > np.timedelta64(0, "ns"):
+            if sign_dt * (endtime - p.time_nextloop) <= np.timedelta64(0, "ns"):
                 return p
 
             # TODO implement below later again
             # try:  # Use next_dt from AdvectionRK45 if it is set
             #     if abs(endtime - p.time_nextloop) < abs(p.next_dt) - 1e-6:
             #         p.next_dt = abs(endtime - p.time_nextloop) * sign_dt
             # except AttributeError:
-            # if abs(endtime - p.time_nextloop) < abs(p.dt) - 1e-6:
-            #     p.dt = abs(endtime - p.time_nextloop) * sign_dt
+            if abs(endtime - p.time_nextloop) <= abs(p.dt):
+                p.dt = abs(endtime - p.time_nextloop) * sign_dt
             res = self._pyfunc(p, self._fieldset, p.time_nextloop)
 
             if res is None:

parcels/particleset.py

@@ -861,8 +861,8 @@ def execute(
         next_output = outputdt if output_file else None
 
         time = start_time
-        while time <= end_time:
-            next_time = time + dt
+        while time < end_time:
+            next_time = min(time + dt, end_time)  # TODO also for time-backward
             res = self._kernel.execute(self, endtime=next_time, dt=dt)
             if res == StatusCode.StopAllExecution:
                 return StatusCode.StopAllExecution

tests/v4/test_particleset.py

@@ -102,6 +102,19 @@ def test_particleset_dt_type(fieldset, dt, expectation):
         pset.execute(runtime=np.timedelta64(10, "s"), dt=dt, pyfunc=DoNothing)
 
 
+def test_pset_starttime_not_multiple_dt(fieldset):
+    times = [0, 1, 2]
+    datetimes = [fieldset.U.time[0].values + np.timedelta64(t, "s") for t in times]
+    pset = ParticleSet(fieldset, lon=[0] * len(times), lat=[0] * len(times), pclass=Particle, time=datetimes)
+
+    def Addlon(particle, fieldset, time):  # pragma: no cover
+        print(f"Addlon: {time} {particle.trajectory}")
+        particle_dlon += particle.dt / np.timedelta64(1, "s")  # noqa
+
+    pset.execute(Addlon, dt=np.timedelta64(2, "s"), runtime=np.timedelta64(8, "s"), verbose_progress=False)
+    assert np.allclose([p.lon_nextloop for p in pset], [8 - t for t in times])
+
+
 @pytest.mark.parametrize(
     "runtime, expectation",
     [