#10752: Matrix pivots are cached, should be immutable
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Reporter: rbeezer | Owner: jason, was
Type: defect | Status: needs_review
Priority: minor | Milestone: sage-4.7
Component: linear algebra | Keywords: matrix pivots
Author: John Palmieri | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Comment(by jhpalmieri):
Here is a new version of the patch. I think this deals with every
instance where something involving the string "pivot" is fetched from the
cache.
There are two other ways to proceed, if we don't like this approach:
- cache the pivots as tuples instead of lists, or
- add a keyword to the "pivots" method just like there currently is for
"nonzero_positions". That is, model the definition after this:
{{{
def nonzero_positions(self, copy=True, column_order=False):
"""
Returns the sorted list of pairs (i,j) such that self[i,j] != 0.
INPUT:
- ``copy`` - (default: True) It is safe to change the
resulting list (unless you give the option copy=False).
}}}
I think the question is, how much of a performance hit is there by copying
the list, and are there times when we want to use the unsafe, but faster
method. I don't know the answer to this. Would the first alternative
(caching a tuple) be any better, or would the cached value need to be
converted to a list frequently enough that it would slow things down?
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10752#comment:2>
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