#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: symbolics | 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: | e195b36b27caeeebcb6f2e69f90b048a9e5b9d51
u/mjo/ticket/12834 | Stopgaps:
Dependencies: |
-------------------------------------+-------------------------------------
Comment (by vdelecroix):
Replying to [comment:26 mjo]:
> Replying to [comment:23 vdelecroix]:
> > 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`?
>
> I guess I wasn't very clear in my commit message =)
>
> The original code was,
>
> {{{
> if any(k in d1 for k in d2):
> k = (k for k in d1 if k in d2).next()
> raise ValueError...
> }}}
>
> The first `any(k in d1 for k in d2)` is probably O(m*n), since it
(potentially) has to look through all of both dictionaries to see if there
are any duplicates. Then,
You are wrong. A dictionary is a hash table not a list. Assuming that
there is no collision this is a O(m) where m=size(d2).
--
Ticket URL: <http://trac.sagemath.org/ticket/12834#comment:28>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sage-trac.
For more options, visit https://groups.google.com/d/optout.
