#10496: The default call method of maps does not do as promised by the
documentation
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Reporter: SimonKing | Owner: robertwb
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.6.2
Component: coercion | Keywords: generic call map
Author: Simon King | Upstream: N/A
Reviewer: David Roe | Merged:
Work_issues: |
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Changes (by SimonKing):
* status: needs_work => needs_review
Comment:
I updated my patch. Here are some timings for different situations.
With the patch:
{{{
sage: R.<x,y> = QQ[]; phi=R.hom([y,x])
# Element in domain
sage: timeit("a=phi(y)")
625 loops, best of 3: 32.3 µs per loop
# Element coerces into domain
sage: timeit("a=phi(5)")
625 loops, best of 3: 51.3 µs per loop
# non-Element that converts into domain
sage: D={(0, 2): -1, (0, 0): -1, (1, 1): 7, (2, 0): 1/3}
sage: phi(D)
-x^2 + 7*x*y + 1/3*y^2 - 1
sage: timeit("a=phi(D)")
625 loops, best of 3: 119 µs per loop
# use pushforward
sage: I = R*[x^2*y^4-2*y^2, 3*x*y-y^3]
sage: phi(I)
Ideal (x^4*y^2 - 2*x^2, -x^3 + 3*x*y) of Multivariate Polynomial Ring in
x, y over Rational Field
sage: timeit("a=phi(I)")
625 loops, best of 3: 164 µs per loop
}}}
The same examples without my patch:
{{{
sage: R.<x,y> = QQ[]; phi=R.hom([y,x])
sage: timeit("a=phi(y)")
625 loops, best of 3: 32.3 µs per loop
sage: timeit("a=phi(5)")
625 loops, best of 3: 37.1 µs per loop
sage: D={(0, 2): -1, (0, 0): -1, (1, 1): 7, (2, 0): 1/3}
sage: phi(D)
---------------------------------------------------------------------------
AttributeError Traceback (most recent call
last)
/home/king/SAGE/work/modules/<ipython console> in <module>()
/mnt/local/king/SAGE/sage-4.6/local/lib/python2.6/site-
packages/sage/categories/map.so in sage.categories.map.Map.__call__
(sage/categories/map.c:3145)()
/mnt/local/king/SAGE/sage-4.6/local/lib/python2.6/site-
packages/sage/rings/morphism.so in
sage.rings.morphism.RingHomomorphism_im_gens._call_
(sage/rings/morphism.c:5761)()
AttributeError: 'dict' object has no attribute '_im_gens_'
sage: I = R*[x^2*y^4-2*y^2, 3*x*y-y^3]
sage: phi(I)
Ideal (x^4*y^2 - 2*x^2, -x^3 + 3*x*y) of Multivariate Polynomial Ring in
x, y over Rational Field
sage: timeit("a=phi(I)")
625 loops, best of 3: 492 µs per loop
}}}
Hence:
* If the argument has the right parent, it is as quick as before.
* If the argument coerces into the domain, it is slower. That is no
surprise, because "not doing coercion" is certainly faster than "doing
coercion", but "not doing coercion" is a bug IMO.
* If the argument is not an element and is not dealt with by pushforward
but converts into the domain, my patch fixes a bug (it is now added as
doctest).
* Calling pushforward works a lot quicker with my patch.
So, I do think that overall it is a progress. I am now starting doctests,
but I think it is ready for review again.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10496#comment:4>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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