#13359: [Performance] Expression::__nonzero__ shouldn't call variables() unless
it
is necessary
---------------------------+------------------------------------------------
Reporter: tkluck | Owner: tbd
Type: enhancement | Status: new
Priority: major | Milestone: sage-5.3
Component: performance | Keywords:
Work issues: | Report Upstream: N/A
Reviewers: | Authors: Timo Kluck
Merged in: | Dependencies:
Stopgaps: |
---------------------------+------------------------------------------------
`Expression::__nonzero__` calls `variables()` in case it needs
assumptions:
{{{
# If assumptions are involved, falsification is more complicated...
need_assumptions = False
vars = self.variables()
if len(vars) > 0:
from sage.symbolic.assumptions import assumptions
assumption_list = assumptions()
if len(assumption_list) > 0:
# do something
}}}
Now, `variables()` is a recursive call that walks down the expression
tree, so you really only want to do this when necessary. The attached
patch changes the order of the `if` statements. In my case that involves
lots of expression manipulations, the running time came down from 2
minutes to 2 seconds.
Background: I'm doing calculations in a `LaurentSeriesRing` over `SR`. The
`LaurentSeriesRing` (and/or its underlying polynomial classes) liberally
call `__nonzero__` on the coefficients to see what the degree or valuation
is, etc. So these comparisons are so much a part of my inner looop that I
had to disable the `test_relation` calls and the Maxima calls. Those are
hacks I cannot submit to the tracker, but this is the next bottleneck.
It should also be possible to improve the performance for `variables` by
calculating it at construction time from the variables of the
subexpressions. I've done some work in that direction, but that's a
different story.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13359>
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