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spec: rows emptied by absence are dropped silently; revisit strict refusal

Abierto
  • ¿Algo no está bien?
#993 2 comentarios 0 reacciones 0 asignados Ver en GitHub

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Evaluación

Dificultad
5/5
Tiempo estimado
Más de una semana
Aptitud para principiantes
30/100
Tipo de issue
Nueva funcionalidad
Claridad
Bastante claro
Estado de actividad
Activo
Stack tecnológico
python
Área
backend

Línea de trabajo

Start with linopy/spec/builder.py::_check_live and run the minimal example from the issue. Read test/test_spec_builder.py::test_absence_takes_the_row_with_it and ::test_a_row_the_data_emptied_of_variables_is_refused to understand the current behavior. Done requires resolving the strictness and warning or edge-policy questions and adding tests for the chosen behavior.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

discussion math-spec

In the long term I would like to have things strict, but for now this is fine. Tracking this so we can readdress it later.

[!NOTE]
The following content was generated by AI.

Describe the feature you'd like to see

With the move to mathspec 0.2.0 in #958, linopy/spec/builder.py::_check_live no longer refuses a constraint row that absence empties. It drops the row silently. This follows mathspec's documented semantics: absence spread through arithmetic "takes the row with it", and the first row of a bare shift "is not built".

Before (0a725f43), such a row raised SpecDataError ("N row(s) hold no variable term"), because a row that silently disappears no longer binds.

The current state after #958:

row behaviour
absent (null) row, e.g. x - shift(x) at the first snapshot dropped silently
bare masked Variable as a term not checked
present row with no variable, e.g. absence: zero against a binding side refused

Strict is the long-term goal. Open questions:

  • Opt-in strictness, e.g. add_spec(..., strict=True), or strict by default with an explicit edge policy in the spec (shift(..., edge=...))?
  • Warn at least with the count of rows dropped per constraint?
  • Does mathspec need a language-level way to state "this row may be dropped", so strict engines can tell intended from accidental absence?

Reasons it is relaxed for now: pypsa.yaml, its netcdf round trip and the spec_pypsa benchmark rely on a bare shift dropping the first snapshot.

Minimal example
import pandas as pd
import xarray as xr

import linopy

linopy.options["semantics"] = "v1"

spec = """
dimensions:
  snapshot: { dtype: int }
variables:
  p:
    dims: [snapshot]
    bounds: { lower: 0 }
constraints:
  no_faster_than_before:
    dims: [snapshot]
    expression: p <= shift(p, along=snapshot, offset=1)
objective: { sense: minimize, expression: sum(p) }
"""
sources = xr.Dataset(coords={"snapshot": pd.Index([0, 1, 2], name="snapshot")})
m = linopy.Model.from_spec(spec, sources)
print(m.constraints["no_faster_than_before"].labels.values)
# [-1  1  2]   -> row at snapshot 0 is dropped without error or warning

Tests pinning the current behaviour: test/test_spec_builder.py::test_absence_takes_the_row_with_it and ::test_a_row_the_data_emptied_of_variables_is_refused.

Lenguaje dominante
Python
Estrellas
259
Forks
89
Merge medio
1 d 18 h
PR fusionados (30 d)
26

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