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spec: rows emptied by absence are dropped silently; revisit strict refusal #993
Description
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.
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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 (0a725f4), 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 warningTests 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.
Activity
chore(spec): migrate to mathspec 0.2.0 from PyPI as the linopy[spec] …
FabianHofmann commentedon Sep 28, 2026
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The following content was generated by AI.
Related hole found while fixing #958 (f186ec8). Since then, arithmetic on present data that turns non-finite is refused (
evaluate.check_finite), so a NaN from0/0orinf - infcan no longer pass as absence.x + sum(a - b, by=...)is caught. But the difference of two grouped sums is not: the model builds silently, with rhs0instead of an error.Likely cause: the grouped sum's
fillna(0)(or its reindexing) hides the non-finite operand before the subtraction is checked. Unverified.FabianHofmann commentedon Sep 28, 2026
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The following content was generated by AI.
The grouped-sum case above is fixed in 81c8eed: data summands a term's constant adds up across a sum or a comparison are now checked too (
x + a - a,x + a >= a,sum - sum,shift - shift). Still not caught: data subtracted after a scaled term, e.g.(x + a) * 2 - 2 * a, since summands are not distributed through*or/.