Move the tof lookup table error threshold to the GenericTofWorkflow

docs/user-guide/tof/dream.ipynb

@@ -743,8 +743,8 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "table = lut_wf.compute(TofLookupTable).array\n",
-    "table.plot() / (sc.stddevs(table) / sc.values(table)).plot(norm=\"log\")"
+    "table = lut_wf.compute(TofLookupTable)\n",
+    "table.plot() / (sc.stddevs(table.array) / sc.values(table.array)).plot(norm=\"log\")"
    ]
   },
   {
@@ -767,10 +767,12 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "lut_wf[LookupTableRelativeErrorThreshold] = 0.01\n",
+    "wf[TofLookupTable] = table\n",
     "\n",
-    "table = lut_wf.compute(TofLookupTable)\n",
-    "table.plot()"
+    "wf[LookupTableRelativeErrorThreshold] = 8.0e-3\n",
+    "\n",
+    "masked_table = wf.compute(ErrorLimitedTofLookupTable)\n",
+    "masked_table.plot()"
    ]
   },
   {
@@ -797,8 +799,6 @@
     "wf[RawDetector[SampleRun]] = ess_beamline.get_monitor(\"detector\")[0]\n",
     "wf[DetectorLtotal[SampleRun]] = Ltotal\n",
     "\n",
-    "wf[TofLookupTable] = table\n",
-    "\n",
     "# Compute time-of-flight\n",
     "tofs = wf.compute(TofDetector[SampleRun])\n",
     "# Compute wavelength\n",
@@ -833,7 +833,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.12.7"
+   "version": "3.12.12"
   }
  },
  "nbformat": 4,

docs/user-guide/tof/wfm.ipynb

@@ -364,7 +364,6 @@
     "lut_wf[DiskChoppers[AnyRun]] = disk_choppers\n",
     "lut_wf[SourcePosition] = source_position\n",
     "lut_wf[LtotalRange] = Ltotal, Ltotal\n",
-    "lut_wf[LookupTableRelativeErrorThreshold] = 0.1\n",
     "lut_wf.visualize(TofLookupTable)"
    ]
   },

src/ess/reduce/time_of_flight/__init__.py

@@ -10,7 +10,6 @@
 from .eto_to_tof import providers
 from .lut import (
     DistanceResolution,
-    LookupTableRelativeErrorThreshold,
     LtotalRange,
     NumberOfSimulatedNeutrons,
     PulsePeriod,
@@ -24,6 +23,8 @@
 )
 from .types import (
     DetectorLtotal,
+    ErrorLimitedTofLookupTable,
+    LookupTableRelativeErrorThreshold,
     MonitorLtotal,
     PulseStrideOffset,
     TimeOfFlightLookupTable,
@@ -42,6 +43,7 @@
     "DetectorLtotal",
     "DiskChoppers",
     "DistanceResolution",
+    "ErrorLimitedTofLookupTable",
     "GenericTofWorkflow",
     "LookupTableRelativeErrorThreshold",
     "LtotalRange",

src/ess/reduce/time_of_flight/eto_to_tof.py

@@ -8,6 +8,7 @@
 """
 
 from collections.abc import Callable
+from dataclasses import asdict
 
 import numpy as np
 import scipp as sc
@@ -34,6 +35,8 @@
 from .resample import rebin_strictly_increasing
 from .types import (
     DetectorLtotal,
+    ErrorLimitedTofLookupTable,
+    LookupTableRelativeErrorThreshold,
     MonitorLtotal,
     PulseStrideOffset,
     ToaDetector,
@@ -99,7 +102,7 @@ def __call__(
 
 
 def _time_of_flight_data_histogram(
-    da: sc.DataArray, lookup: TofLookupTable, ltotal: sc.Variable
+    da: sc.DataArray, lookup: ErrorLimitedTofLookupTable, ltotal: sc.Variable
 ) -> sc.DataArray:
     # In NeXus, 'time_of_flight' is the canonical name in NXmonitor, but in some files,
     # it may be called 'tof' or 'frame_time'.
@@ -204,7 +207,7 @@ def _guess_pulse_stride_offset(
 
 def _prepare_tof_interpolation_inputs(
     da: sc.DataArray,
-    lookup: TofLookupTable,
+    lookup: ErrorLimitedTofLookupTable,
     ltotal: sc.Variable,
     pulse_stride_offset: int | None,
 ) -> dict:
@@ -298,7 +301,7 @@ def _prepare_tof_interpolation_inputs(
 
 def _time_of_flight_data_events(
     da: sc.DataArray,
-    lookup: TofLookupTable,
+    lookup: ErrorLimitedTofLookupTable,
     ltotal: sc.Variable,
     pulse_stride_offset: int | None,
 ) -> sc.DataArray:
@@ -396,9 +399,36 @@ def monitor_ltotal_from_straight_line_approximation(
     )
 
 
+def mask_large_uncertainty_in_lut(
+    table: TofLookupTable, error_threshold: LookupTableRelativeErrorThreshold
+) -> ErrorLimitedTofLookupTable:
+    """
+    Mask regions in the time-of-flight lookup table with large uncertainty using NaNs.
+
+    Parameters
+    ----------
+    table:
+        Lookup table with time-of-flight as a function of distance and time-of-arrival.
+    error_threshold:
+        Threshold for the relative standard deviation (coefficient of variation) of the
+        projected time-of-flight above which values are masked.
+    """
+    # TODO: The error threshold could be made dependent on the time-of-flight or
+    # distance, instead of being a single value for the whole table.
+    da = table.array
+    relative_error = sc.stddevs(da.data) / sc.values(da.data)
+    mask = relative_error > sc.scalar(error_threshold)
+    return ErrorLimitedTofLookupTable(
+        **{
+            **asdict(table),
+            "array": sc.where(mask, sc.scalar(np.nan, unit=da.unit), da),
+        }
+    )
+
+
 def _compute_tof_data(
     da: sc.DataArray,
-    lookup: TofLookupTable,
+    lookup: ErrorLimitedTofLookupTable,
     ltotal: sc.Variable,
     pulse_stride_offset: int,
 ) -> sc.DataArray:
@@ -417,7 +447,7 @@ def _compute_tof_data(
 
 def detector_time_of_flight_data(
     detector_data: RawDetector[RunType],
-    lookup: TofLookupTable,
+    lookup: ErrorLimitedTofLookupTable,
     ltotal: DetectorLtotal[RunType],
     pulse_stride_offset: PulseStrideOffset,
 ) -> TofDetector[RunType]:
@@ -452,7 +482,7 @@ def detector_time_of_flight_data(
 
 def monitor_time_of_flight_data(
     monitor_data: RawMonitor[RunType, MonitorType],
-    lookup: TofLookupTable,
+    lookup: ErrorLimitedTofLookupTable,
     ltotal: MonitorLtotal[RunType, MonitorType],
     pulse_stride_offset: PulseStrideOffset,
 ) -> TofMonitor[RunType, MonitorType]:
@@ -487,7 +517,7 @@ def monitor_time_of_flight_data(
 
 def detector_time_of_arrival_data(
     detector_data: RawDetector[RunType],
-    lookup: TofLookupTable,
+    lookup: ErrorLimitedTofLookupTable,
     ltotal: DetectorLtotal[RunType],
     pulse_stride_offset: PulseStrideOffset,
 ) -> ToaDetector[RunType]:
@@ -585,4 +615,5 @@ def providers() -> tuple[Callable]:
         detector_time_of_arrival_data,
         detector_wavelength_data,
         monitor_wavelength_data,
+        mask_large_uncertainty_in_lut,
     )

src/ess/reduce/time_of_flight/lut.py

@@ -7,7 +7,6 @@
 from dataclasses import dataclass
 from typing import NewType
 
-import numpy as np
 import sciline as sl
 import scipp as sc
 
@@ -112,13 +111,6 @@ class SimulationResults:
 smaller if the pulse period is not an integer multiple of the time resolution.
 """
 
-
-LookupTableRelativeErrorThreshold = NewType("LookupTableRelativeErrorThreshold", float)
-"""
-Threshold for the relative standard deviation (coefficient of variation) of the
-projected time-of-flight above which values are masked.
-"""
-
 PulsePeriod = NewType("PulsePeriod", sc.Variable)
 """
 Period of the source pulses, i.e., time between consecutive pulse starts.
@@ -144,26 +136,6 @@ class SimulationResults:
 """
 
 
-def _mask_large_uncertainty(table: sc.DataArray, error_threshold: float):
-    """
-    Mask regions with large uncertainty with NaNs.
-    The values are modified in place in the input table.
-
-    Parameters
-    ----------
-    table:
-        Lookup table with time-of-flight as a function of distance and time-of-arrival.
-    error_threshold:
-        Threshold for the relative standard deviation (coefficient of variation) of the
-        projected time-of-flight above which values are masked.
-    """
-    # Finally, mask regions with large uncertainty with NaNs.
-    relative_error = sc.stddevs(table.data) / sc.values(table.data)
-    mask = relative_error > sc.scalar(error_threshold)
-    # Use numpy for indexing as table is 2D
-    table.values[mask.values] = np.nan
-
-
 def _compute_mean_tof(
     simulation: BeamlineComponentReading,
     distance: sc.Variable,
@@ -235,7 +207,6 @@ def make_tof_lookup_table(
     time_resolution: TimeResolution,
     pulse_period: PulsePeriod,
     pulse_stride: PulseStride,
-    error_threshold: LookupTableRelativeErrorThreshold,
 ) -> TofLookupTable:
     """
     Compute a lookup table for time-of-flight as a function of distance and
@@ -258,9 +229,6 @@ def make_tof_lookup_table(
     pulse_stride:
         Stride of used pulses. Usually 1, but may be a small integer when
         pulse-skipping.
-    error_threshold:
-        Threshold for the relative standard deviation (coefficient of variation) of the
-        projected time-of-flight above which values are masked.
 
     Notes
     -----
@@ -387,17 +355,13 @@ def make_tof_lookup_table(
         },
     )
 
-    # In-place masking for better performance
-    _mask_large_uncertainty(table, error_threshold)
-
     return TofLookupTable(
         array=table,
         pulse_period=pulse_period,
         pulse_stride=pulse_stride,
         distance_resolution=table.coords["distance"][1] - table.coords["distance"][0],
         time_resolution=table.coords["event_time_offset"][1]
         - table.coords["event_time_offset"][0],
-        error_threshold=error_threshold,
         choppers=sc.DataGroup(
             {k: sc.DataGroup(ch.as_dict()) for k, ch in simulation.choppers.items()}
         )
@@ -490,7 +454,6 @@ def TofLookupTableWorkflow():
             PulseStride: 1,
             DistanceResolution: sc.scalar(0.1, unit="m"),
             TimeResolution: sc.scalar(250.0, unit='us'),
-            LookupTableRelativeErrorThreshold: 0.1,
             NumberOfSimulatedNeutrons: 1_000_000,
             SimulationSeed: None,
             SimulationFacility: 'ess',

src/ess/reduce/time_of_flight/types.py

@@ -34,9 +34,6 @@ class TofLookupTable:
     """Resolution of the distance coordinate in the lookup table."""
     time_resolution: sc.Variable
     """Resolution of the time_of_arrival coordinate in the lookup table."""
-    error_threshold: float
-    """The table is masked with NaNs in regions where the standard deviation of the
-    time-of-flight is above this threshold."""
     choppers: sc.DataGroup | None = None
     """Chopper parameters used when generating the lookup table, if any. This is made
     optional so we can still support old lookup tables without chopper info."""
@@ -54,12 +51,24 @@ def plot(self, *args, **kwargs) -> Any:
 """Lookup table giving time-of-flight as a function of distance and time of arrival
 (alias)."""
 
+
+class ErrorLimitedTofLookupTable(TofLookupTable):
+    """Lookup table that is masked with NaNs in regions where the standard deviation of
+    the time-of-flight is above a certain threshold."""
+
+
 PulseStrideOffset = NewType("PulseStrideOffset", int | None)
 """
 When pulse-skipping, the offset of the first pulse in the stride. This is typically
 zero but can be a small integer < pulse_stride. If None, a guess is made.
 """
 
+LookupTableRelativeErrorThreshold = NewType("LookupTableRelativeErrorThreshold", float)
+"""
+Threshold for the relative standard deviation (coefficient of variation) of the
+projected time-of-flight above which values are masked.
+"""
+
 
 class DetectorLtotal(sl.Scope[RunType, sc.Variable], sc.Variable):
     """Total path length of neutrons from source to detector (L1 + L2)."""

src/ess/reduce/time_of_flight/workflow.py

@@ -7,33 +7,34 @@
 
 from ..nexus import GenericNeXusWorkflow
 from . import eto_to_tof
-from .types import PulseStrideOffset, TofLookupTable, TofLookupTableFilename
+from .types import (
+    LookupTableRelativeErrorThreshold,
+    PulseStrideOffset,
+    TofLookupTable,
+    TofLookupTableFilename,
+)
 
 
-def load_tof_lookup_table(
-    filename: TofLookupTableFilename,
-) -> TofLookupTable:
+def load_tof_lookup_table(filename: TofLookupTableFilename) -> TofLookupTable:
     """Load a time-of-flight lookup table from an HDF5 file."""
     table = sc.io.load_hdf5(filename)
 
     # Support old format where the metadata were stored as coordinates of the DataArray.
     # Note that no chopper info was saved in the old format.
     if isinstance(table, sc.DataArray):
+        to_be_dropped = {
+            "pulse_period",
+            "pulse_stride",
+            "distance_resolution",
+            "time_resolution",
+            "error_threshold",
+        } & set(table.coords)
         table = {
-            "array": table.drop_coords(
-                [
-                    "pulse_period",
-                    "pulse_stride",
-                    "distance_resolution",
-                    "time_resolution",
-                    "error_threshold",
-                ]
-            ),
+            "array": table.drop_coords(to_be_dropped),
             "pulse_period": table.coords["pulse_period"],
             "pulse_stride": table.coords["pulse_stride"].value,
             "distance_resolution": table.coords["distance_resolution"],
             "time_resolution": table.coords["time_resolution"],
-            "error_threshold": table.coords["error_threshold"].value,
         }
 
     return TofLookupTable(**table)
@@ -87,5 +88,6 @@ def GenericTofWorkflow(
 
     # Default parameters
     wf[PulseStrideOffset] = None
+    wf[LookupTableRelativeErrorThreshold] = float('inf')
 
     return wf

tests/time_of_flight/lut_test.py

@@ -159,7 +159,6 @@ def test_lut_workflow_computes_table_with_choppers():
     )
     wf[time_of_flight.DistanceResolution] = sc.scalar(0.1, unit='m')
     wf[time_of_flight.TimeResolution] = sc.scalar(250.0, unit='us')
-    wf[time_of_flight.LookupTableRelativeErrorThreshold] = 2e3
 
     table = wf.compute(time_of_flight.TofLookupTable)
 
@@ -194,7 +193,6 @@ def test_lut_workflow_computes_table_with_choppers_full_beamline_range():
     )
     wf[time_of_flight.DistanceResolution] = sc.scalar(0.1, unit='m')
     wf[time_of_flight.TimeResolution] = sc.scalar(250.0, unit='us')
-    wf[time_of_flight.LookupTableRelativeErrorThreshold] = 2e3
 
     table = wf.compute(time_of_flight.TofLookupTable)