Reject non-positive inputs in wpm() (#1382)#1385
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brendancol merged 1 commit intomainfrom Apr 30, 2026
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`wpm` computes `prod(x_i ** w_i)`, which is undefined for `x_i <= 0` when `w_i` is non-integer. A zero base collapses the product to zero and masks upstream standardization bugs; a negative base produces NaN with no warning. The function docstring claimed inputs should be standardized 0-1 but no runtime check enforced it. Add `_check_wpm_positive` to scan each criterion's data and raise `ValueError` naming any variable whose minimum is `<= 0`. NaN values still propagate, preserving the documented behaviour exercised by `test_wpm_nan`. Update the existing zero/all-zero tests to assert the new error and add three more tests covering negative inputs, error text, and the positive-path baseline. Sibling Cat 3 follow-up to #1311 / #1312.
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Summary
Closes #1382.
wpmcomputesprod(x_i ** w_i). For non-integer weights this is only well-defined whenx_i > 0: a zero base collapses the whole product to zero and masks upstream bugs in standardization, and a negative base produces NaN with no error. The docstring said inputs should be standardized 0-1 but nothing enforced that at runtime.Sibling Cat 3 follow-up to the NaN-weight fix in #1311 / #1312, which flagged this case as deferred.
Changes
xrspatial/mcda/combine.py: added_check_wpm_positive, called fromwpmafter the existing weight checks. It runsnanminper variable (eager compute for dask, since correctness here is worth one extra pass) and raisesValueErrorlisting every variable whose minimum is<= 0. NaN values pass through, so the documented NaN-propagation behaviour is preserved. Updated the docstring to spell out the positivity requirement.xrspatial/tests/test_mcda.py: rewrote the two tests that asserted zero-collapses-to-zero (test_zero_value_kills_product,test_all_zeros) to expect the new error, and added three more tests: negative input, error message names the offending variable, and a positive-path baseline.Test plan
pytest xrspatial/tests/test_mcda.py-- 169/169 passValueErrornaming'a'and'b'test_wpm_nanpasses)