#5417: Fix some more deepcopy issues (followup to #5403)
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Reporter: mabshoff | Owner: justin
Type: defect | Status: new
Priority: major | Milestone: sage-3.4
Component: quadratic forms | Keywords:
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Comment(by tornaria):
The patch in #5403 fixes the function {{{scale_by_factor}}} in
{{{quadratic_form__variable_substitutions.py}}}, by replacing the use of
{{{copy.deepcopy}}} + {{{__init__}}} by a call to the constructor.
The issue with this is that the caches for some functions are copied,
hence the results may be incorrect. There seem to be more instances of
this bug in the quadratic_forms code, hence this ticket, but that one is
the only one currently triggered by the following doctest (this only
happens ''after'' applying the {{{import *}}} fix in #5403 without the
{{{deepcopy}}} fix):
{{{
sage: Q = QuadraticForm(ZZ, 3, [2, -2, 0, 3, -5, 4])
sage: Q.jordan_blocks_in_unimodular_list_by_scale_power(2)
Traceback (most recent call last):
...
TypeError: Oops! The given quadratic form has a Jordan component
with a negative scale exponent!
This routine requires an integer-matrix quadratic form for the
output indexing to work properly!
sage:
Q.scale_by_factor(2).jordan_blocks_in_unimodular_list_by_scale_power(2)
[Quadratic form in 2 variables over Integer Ring with
coefficients:
[ 0 2 ]
[ * 0 ]
,
Quadratic form in 0 variables over Integer Ring with coefficients:
,
Quadratic form in 1 variables over Integer Ring with coefficients:
[ 345 ]
]
}}}
In this example, after the first call to
{{{jordan_blocks_in_unimodular_list_by_scale_power}}}, the result is
cached, and the function {{{scale_by_factor}}} copies this cached result,
so that the second call returns the answer for the original quadratic
form.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5417#comment:1>
Sage <http://sagemath.org/>
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