On Sep 10, 2009, at 9:10 AM, Jason Grout wrote:
> I was working on a calculus tutorial/primer on Sage yesterday
> (http://sagenb.org/home/pub/791/). I realized how annoyed I get with
> always having to specify the solution_dict parameter to solve in order
> to substitute values back into another expression. Almost every
> time I
> use solve, I immediately substitute the values back into some other
> expression. Having to write solution_dict=True all the time is (a)
> hard
> to remember and (b) inconvenient. Part of the reason for (a) is
> that I
> think "solution_dict" is a long and not very obvious name (I think I
> wrote the solution_dict patch, so it's my fault! Sorry for the bad
> name!).
>
> Somewhere, a while ago, I remember there being a consensus (with small
> voter turnout) that solution_dict should default to True (I can't find
> the thread on this, though). That is effectively what Mathematica
> does,
> for example. Mathematica returns a list of rules, which print as
> {x->3,
> y->4}, and which are very easy and natural to substitute back into
> other
> expressions.
>
> I wonder if we could either:
>
> (a) make solution_dict default to True (and maybe transition to some
> sort of better-named keyword argument?)
It would need to be more robust when it can't actually solve things:
sage: solve([x==sin(x)], x, solution_dict=True)
------------------------------------------------------------
Traceback (most recent call last):
File "<ipython console>", line 1, in <module>
File "/Users/robert/sage/sage-4.0/local/lib/python2.6/site-
packages/sage/symbolic/relation.py", line 509, in solve
sol_dict=[dict([[eq.left(),eq.right()] for eq in solution]) for
solution in sol_list]
TypeError: 'sage.symbolic.expression.Expression' object is not iterable
> * this may break lots of code, so maybe ought to be put off
> until 5.0.
>
> (b) make .subs() and maybe the __call__ method of a symbolic
> expression
> take the output of solve as-is and try to do something intelligent
> (i.e., see if the lhs of each equation is a single variable, and
> substitute in the right side)
>
> What do you think?
I say go we should do (b) whether or not we do (a), but perhaps only
if the rhs does not contain the variables of the lhs.
- Robert
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