Restrict number of time points for non-0D field time monitors

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 - `run_time` of the adjoint simulation is set more robustly based on the adjoint sources and the forward simulation `run_time` as `sim_fwd.run_time + c / fwdith_adj` where `c=10`.
+- `FieldTimeMonitor` restriction to record at a maximum of 5000 time steps if the monitor is not zero-dimensional, to avoid creating unnecessarily large amounts of data.
 
 ### Fixed
 - `tidy3d.plugins.design.Results` store the `BatchData` for batch runs in the `.batch_data` field.

tests/test_components/test_simulation.py

@@ -1850,6 +1850,39 @@ def test_error_large_monitors(monitor):
         sim_large.validate_pre_upload()
 
 
+def test_error_max_time_monitor_steps():
+    """Test if a time monitor with too many time steps causes pre upload error."""
+
+    sim = td.Simulation(
+        size=(5, 5, 5),
+        run_time=1e-12,
+        grid_spec=td.GridSpec.uniform(dl=0.01),
+        sources=[
+            td.ModeSource(
+                size=(0.1, 0.1, 0),
+                direction="+",
+                source_time=td.GaussianPulse(freq0=2e14, fwidth=0.1e14),
+            )
+        ],
+    )
+
+    # simulation with a 0D time monitor should not error
+    monitor = td.FieldTimeMonitor(center=(0, 0, 0), size=(0, 0, 0), name="time")
+    sim = sim.updated_copy(monitors=[monitor])
+    sim.validate_pre_upload()
+
+    # 1D monitor should error
+    with pytest.raises(SetupError):
+        monitor = monitor.updated_copy(size=(1, 0, 0))
+        sim = sim.updated_copy(monitors=[monitor])
+        sim.validate_pre_upload()
+
+    # setting a large enough interval should again not error
+    monitor = monitor.updated_copy(interval=20)
+    sim = sim.updated_copy(monitors=[monitor])
+    sim.validate_pre_upload()
+
+
 def test_monitor_num_cells():
     """Test the computation of number of cells in monitor."""
     sim = td.Simulation(

tidy3d/components/simulation.py

@@ -33,7 +33,7 @@
 from .source import CustomCurrentSource, CustomSourceTime, ContinuousWave
 from .source import TFSF, Source, ModeSource
 from .monitor import MonitorType, Monitor, FreqMonitor, SurfaceIntegrationMonitor
-from .monitor import AbstractModeMonitor, FieldMonitor, TimeMonitor
+from .monitor import AbstractModeMonitor, FieldMonitor, TimeMonitor, FieldTimeMonitor
 from .monitor import PermittivityMonitor, DiffractionMonitor, AbstractFieldProjectionMonitor
 from .monitor import FieldProjectionAngleMonitor, FieldProjectionKSpaceMonitor
 from .lumped_element import LumpedElementType, LumpedResistor
@@ -71,11 +71,14 @@
 # maximum number of sources
 MAX_NUM_SOURCES = 1000
 
-# maximum numbers of simulation parameters
+# restrictions on simulation number of cells and number of time steps
 MAX_TIME_STEPS = 1e7
 WARN_TIME_STEPS = 1e6
 MAX_GRID_CELLS = 20e9
 MAX_CELLS_TIMES_STEPS = 1e16
+
+# monitor warnings and restrictions
+MAX_TIME_MONITOR_STEPS = 5000  # does not apply to 0D monitors
 WARN_MONITOR_DATA_SIZE_GB = 10
 MAX_MONITOR_INTERNAL_DATA_SIZE_GB = 50
 MAX_SIMULATION_DATA_SIZE_GB = 50
@@ -1743,6 +1746,7 @@ def validate_pre_upload(self, source_required: bool = True) -> None:
         self._validate_datasets_not_none()
         self._validate_tfsf_structure_intersections()
         self._warn_time_monitors_outside_run_time()
+        self._validate_time_monitors_num_steps()
         _ = self.volumetric_structures
         log.end_capture(self)
         if source_required and len(self.sources) == 0:
@@ -1854,6 +1858,21 @@ def warn_mode_size(monitor: AbstractModeMonitor, msg_header: str, custom_loc: Li
                     custom_loc = ["monitors", mnt_ind]
                     warn_mode_size(monitor=monitor, msg_header=msg_header, custom_loc=custom_loc)
 
+    def _validate_time_monitors_num_steps(self) -> None:
+        """Raise an error if non-0D time monitors have too many time steps."""
+        for monitor in self.monitors:
+            if not isinstance(monitor, FieldTimeMonitor) or len(monitor.zero_dims) == 3:
+                continue
+            num_time_steps = monitor.num_steps(self.tmesh)
+            if num_time_steps > MAX_TIME_MONITOR_STEPS:
+                raise SetupError(
+                    f"Time monitor '{monitor.name}' records at {num_time_steps} time steps, which "
+                    f"is larger than the maximum allowed value of {MAX_TIME_MONITOR_STEPS} when "
+                    "the monitor is not zero-dimensional. Change the geometry to a point monitor, "
+                    "or use 'start', 'stop', and 'interval' to reduce the number of time steps "
+                    "at which the monitor stores data."
+                )
+
     @cached_property
     def monitors_data_size(self) -> Dict[str, float]:
         """Dictionary mapping monitor names to their estimated storage size in bytes."""