solve with solution_dict=True doesn't always return a list

[mhampton]

As pointed out in a post on sage-support:

var('x')
g(x)=0
print solve(g(x)==0,x)
print solve(g(x)==0,x,solution_dict=True) 

gives

[x == r1]
{x: r1}

It should be [{x: r1}] to be consistent.

[leif]

Yep:

       * ``solution_dict`` - bool (default: False); if True or non-zero,
         return a list of dictionaries containing the solutions. If there
         are no solutions, return an empty list (rather than a list
         containing an empty dictionary). Likewise, if there's only a
         single solution, return a list containing one dictionary with
         that solution.

A doctest for a similar case got deleted by a reviewer, which still works though:

sage: solve([x+y==6, x-y==4], x, y, solution_dict=-1)
[{y: 1, x: 5}]

And also the following works as expected:

sage: solve([x==0],x,solution_dict=True)
[{x: 0}]

(Sage 4.7.1.{alpha2,rc0})

[leif]

The attached patch fixes the inconsistency and adds a doctest for the case given.

I've removed superfluous parentheses (and white space) and also converted some tabs to spaces. (I thought the merge script would reject patches introducing new tabs after all got converted a while ago.)

[leif]

Hmmm,

ans = [ {x: self.parent().var('r1')} ]

would perhaps have been a bit more readable...

[leif]

Sage library patch. (Updated version.) Based on Sage 4.7.1.rc0.

[leif]

Replying to leif:

[...] would perhaps have been a bit more readable.

I've updated the patch to directly construct the solution dictionary.

(Leif doesn't work without coffee.)

---

Hey patchbot, apply: trac_11618-fix_solution_dict_for_infinitely_many_solutions.sagelib.patch !

[leif]

The dependency I've added is (more or less) just for the patchbot. (#8553 was merged into Sage 4.7.1.alpha2.)

[kcrisman]

Thanks for posting this patch - I'll try to take a look at this (relatively) soon, as it looks straightforward.

[kcrisman]

Patch looks good. Performs as advertised. Thanks!