#12834: Modify subs so that it can accept multiple equations just like subs_expr
-------------------------------------+-------------------------------------
Reporter: JoalHeagney | Owner: AlexGhitza
Type: enhancement | Status: needs_work
Priority: minor | Milestone: sage-6.4
Component: algebra | Resolution:
Keywords: subs algebra | Merged in:
solving | Reviewers: Vincent Delecroix,
Authors: Michael Orlitzky, | Michael Orlitzky
Vincent Delecroix | Work issues:
Report Upstream: N/A | Commit:
Branch: | 24b98a061c140e9f76b171eb3dd1be0fa44d36b8
u/mjo/ticket/12834 | Stopgaps:
Dependencies: |
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Changes (by vdelecroix):
* status: needs_review => needs_work
Comment:
Hello,
I do not agree with your `05492f4` and `0d34382`. First of all, if
something is wrong, then it is not a big deal to go through the
dictionaries again. Your version is way much too complicated. Please do
something along
{{{
dup = [k for k in d2 if k in d1]
if dup:
k = min(dup)
msg = "duplicate substitution for {}, got values {} and {}"
raise ValueError(msg.format(k, d1[k], d2[k]))
}}}
And you can remark that I iterated over `d2` and this was intentional. The
dictionary `d1` is intended to be large compared to `d2` (think about
`expr.subs(u == 18, v == 15, w == 19, x == 1, y == 2, z == 3)`). In your
commit you reversed that. And you should know that to get the minimum of a
list you do not need to sort it ;-) Was the call to `sorted` intentional
compared to `min`?
If you have access to `Maple/Mathematica` I would be curious to know what
they do for
{{{
sage: (x + x^2 + x^4).subs(x + x^2 == 2)
}}}
The other changes are fine to me.
Vincent
--
Ticket URL: <http://trac.sagemath.org/ticket/12834#comment:23>
Sage <http://www.sagemath.org>
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