#16836: __neg__ fails in CartesianProduct of CombinatorialFreeModule
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Reporter: cnassau | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.4
Component: categories | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by cnassau):
The fix appears to be quite simple:
{{{#!diff
--- a/src/sage/categories/additive_magmas.py
+++ b/src/sage/categories/additive_magmas.py
@@ -918,8 +918,8 @@ class AdditiveMagmas(Category_singleton):
...
AssertionError
"""
- return self.parent()(
- -x for x in self.cartesian_factors())
+ return self.parent()._cartesian_product_of_elements(
+ [-x for x in self.cartesian_factors()])
}}}
This breaks a doctest, however:
{{{
File "src/sage/categories/additive_magmas.py", line 903, in
sage.categories.additive_magmas.AdditiveMagmas.AdditiveUnital.CartesianProducts.ElementMethods.__neg__
Failed example:
-c
Expected:
Traceback (most recent call last):
...
ValueError: Value -42 in not in Non negative integers.
Got:
(-1, -42, -1.00000000000000)
}}}
The fix for that doctest would be to move a sanity check from `_neg_` to
`CartesianProduct._cartesian_product_of_elements`. That then breaks a
design-comment in the latter routine about being optimized for speed.
Alternatively, the doctest could be removed (my choice). We don't want an
implicit sanity-check whenever we negate an element of a cartesian
product.
This is therefore the sort of code/bug that only the original author can
fix.
--
Ticket URL: <http://trac.sagemath.org/ticket/16836#comment:1>
Sage <http://www.sagemath.org>
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