Opened 4 years ago

Last modified 3 years ago

#23376 closed defect

Equality testing of genera of quadratic forms over ZZ changes the genus and produces false results — at Initial Version

Reported by: sbrandhorst Owned by:
Priority: major Milestone: sage-8.0
Component: quadratic forms Keywords: sd87, Genus, sd91
Cc: Merged in:
Authors: Simon Brandhorst Reviewers:
Report Upstream: N/A Work issues:
Branch: Commit:
Dependencies: Stopgaps:

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sage: D4=QuadraticForm?(Matrix(ZZ,4,4,[2,0,0,-1,0,2,0,-1,0,0,2,-1,-1,-1,-1,2])) sage: G=D4.global_genus_symbol() sage: sage.quadratic_forms.genera.genus.is_GlobalGenus(G) True sage: G==copy(G) True sage: sage.quadratic_forms.genera.genus.is_GlobalGenus(G) False

The reason is that various functions unintentionally modify their input. Since a genus consists of lists containing lists, functions do just copy the lists but not deepcopy.

For example sage.quadratic_forms.genera.genus.canonical_2_adic_reduction

modifies its input which does not seem to be intended.

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