On Wed, Apr 20, 2011 at 12:16 PM, Aaron S. Meurer <[email protected]> wrote:
>
> On Apr 20, 2011, at 1:04 PM, Mateusz Paprocki wrote:
>
> Hi,
>
> On 20 April 2011 11:55, Aaron S. Meurer <[email protected]> wrote:
>>
>> The Solution class is indeed a good idea.
>>
>> I think it would be best to have a unified data structure independent of
>> the number of solutions. The reason is that it is not clear from the outset
>> how many solutions an equation or system of equations will have. That is
>> why I think it would be better to have a list always or a dictionary always
>> (or a list of dictionaries always). The list of dictionaries idea is one of
>> the better ones, in my opinion.
>
> This is what Mathematica does (for example) (it gives a list of rules, which
> is a list of dicts in Python's terminology). There is one more issue that
> has to be taken into account: currently it's not easy to substitute results
> from solve() back to the original equation/set of equations (in a systematic
> way).
>
> If you have a list of dictionaries, you can just do
> sol = solve(expr, vars)
> expr.subs(sol[0])
> expr.subs(sol[1])
> …
> or just
> [expr.subs(i) for i in sol]
> because subs works with a dictionary. Actually, looking at it this way,
> this data structure is far superior to any of the others.
I agree that the list of dicts is a good option for this.
> And this is another advantage that a Solution class could offer. We could
> just make expr.subs(Solution) work as you would expect it to.
> Aaron Meurer
>
>
>>
>> Aaron Meurer
>>
>> On Apr 20, 2011, at 3:57 AM, Alexey U. Gudchenko wrote:
>>
>> > 20.04.2011 11:45, Chris Smith пишет:
>> >>> Solution class is needed indeed. Also, to recognize correctly the
>> >>> number of solutions with the help of `len` procedure. If we return the
>> >>> dictionary it is not clear:
>> >>>
>> >>>>>> len({x: 3, y: 2})
>> >>> 2
>> >>>>>> [{x: 3, y: 2}, {x: 8, y: -3}]
>> >>> 2 (too)
>> >>>
>> >>
>> >> Until a Solution class exists, the multi-solution case should come back
>> >> like the single solution: as a list.
>> >> So solutions will look like `[1]`, ` [1, 2]`, `[{x: 3, y: 2}]` or `[{x:
>> >> 3, y: 2}, {x: 8, y: -3}]`.
>> >>
>> >
>> > May be....
>> > As temporary solution.
>> >
>> > But if a Solution class will exists, it is not necessary to result a
>> > list if one solution only. I have pointed out an advantage of this case
>> > (strict typified interface of function definition) and disadvantage (not
>> > convenient for end-user).
>> >
>> > But I can't decide it, because I do not know exactly the politic way in
>> > SumPy for this cases (how to manage with variant results).
>> >
>> > My opinion that it would be rather suitable:
>> > `1`, ` [1, 2]`, `{x: 3, y: 2}` or `[{x: 3, y: 2}, {x: 8, y: -3}]`
>> >
>> > If Solution class exist, then I check type (list of Solutions or
>> > Solution itself) with easy.
>> >
>> > Also, taking into account Mateusz's notes (e.g. about sorting of
>> > dictinary) I think that the issue for Solution class should be created
>> > in issue-tracker too.
>> >
>> > --
>> > Alexey U.
>> >
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>>
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>
> Mateusz
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--
Brian E. Granger
Cal Poly State University, San Luis Obispo
[email protected] and [email protected]
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