Added more information to error when drive cycle starts at t>0

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Bug Fixes
 
+- updated `_steps_util.py` to throw a specific exception when drive cycle starts at t>0
 - Updated `plot_voltage_components.py` to support both `Simulation` and `Solution` objects. Added new methods in both `Simulation` and `Solution` classes for allow the syntax `simulation.plot_voltage_components` and `solution.plot_voltage_components`. Updated `test_plot_voltage_components.py` to reflect these changes ([#3723](https://github.com/pybamm-team/PyBaMM/pull/3723)).
 - The SEI thickness decreased at some intervals when the 'electron-migration limited' model was used. It has been corrected ([#3622](https://github.com/pybamm-team/PyBaMM/pull/3622))
 

docs/source/api/experiment/experiment_steps.rst

@@ -1,7 +1,7 @@
 Experiment step functions
 =========================
 
-The following functions can be used to define steps in an experiment.
+The following functions can be used to define steps in an experiment. Note that the drive cycle must start at t=0
 
 .. autofunction:: pybamm.step.string
 

pybamm/experiment/step/_steps_util.py

@@ -120,8 +120,15 @@ def __init__(
                 t, y = value[:, 0], value[:, 1]
                 self.duration = t.max()
 
+            # Check that drive cycle starts at t=0
+            if t[0] > 0:
+                raise ValueError("Drive cycle must start at t=0")
+
             self.value = pybamm.Interpolant(
-                t, y, pybamm.t - pybamm.InputParameter("start time")
+                t,
+                y,
+                pybamm.t - pybamm.InputParameter("start time"),
+                name="Drive Cycle",
             )
             self.period = np.diff(t).min()
         else:

tests/unit/test_experiments/test_experiment_steps.py

@@ -5,6 +5,7 @@
 import unittest
 import numpy as np
 from datetime import datetime
+from pybamm.experiment.step import _Step
 
 
 class TestExperimentSteps(unittest.TestCase):
@@ -276,6 +277,13 @@ def neg_stoich_cutoff(variables):
         self.assertEqual(event.name, "Negative stoichiometry cut-off [experiment]")
         self.assertEqual(event.expression, 2)
 
+    def test_drive_cycle_start_time(self):
+        # An example where start_time t>0
+        t = np.array([[1, 1], [2, 2], [3, 3]])
+
+        with self.assertRaisesRegex(ValueError, "Drive cycle must start at t=0"):
+            _Step("current", t)
+
 
 if __name__ == "__main__":
     print("Add -v for more debug output")