Yeah I initially thought of doing this - but say I want to do:
y = Symbol('y')
domain = And(-oo < y, y < oo)
print domain
>>> True
Which is unfortunate! Since having a domain over all real numbers is not
uncommon
On 25 July 2013 02:17, Aaron Meurer <[email protected]> wrote:
> You can already write inequalities, and combine them using And and Or:
>
> In [25]: x > 0
> Out[25]: x > 0
>
> In [26]: Or(x > 0, x < 1)
> Out[26]: x > 0 ∨ x < 1
>
> In [27]: Or(x > 0, x < 1).subs(x, 2)
> Out[27]: True
>
> If all you care about is getting it to work mathematically (i.e., with
> subs), then you can get pretty far with this. It won't work with the
> assumptions system, though, and it can get messy fast, especially if
> you do care about printing.
>
> I think what we need is just a Contains object, subclassing from
> Boolean, which would work like Contains(x, Set), where Set is any set
> from the sets module. It shouldn't be too hard to write something like
> this. Basic functionality just needs to check set.contains for
> evaluation, and implement basic pretty printing with ∈.
>
> One issue is that there still isn't a very clear separation between
> boolean and symbolic objects
> (https://code.google.com/p/sympy/issues/detail?id=1887). And there are
> of course issues with the assumptions system in general.
>
> Aaron Meurer
>
>
> On Wed, Jul 24, 2013 at 6:34 AM, Stefan Krastanov
> <[email protected]> wrote:
> > It depends what exactly you want to do.
> >
> > If you need it just for typography purposes (e.g. writing something in
> > IPython notebook and wanting to print the expression) you are using sympy
> > incorrectly. SymPy is not a typography library. (if you insists there are
> > hacks to do it)
> >
> > On the other hand quite frequently you need this for meaningful
> mathematics.
> >
> > - if you want to work on polynomials and do certain operations (finding
> > roots, etc) over a given field, you do this by specifying the field
> during
> > the creation of the polynomial.
> >
> > - there is some work in progress to be able to do the same for matrices,
> but
> > it is not ready.
> >
> > - in general, there is the assumption module. It is a bit of a mess,
> because
> > we have an old and a new assumption module and we try to move to the new
> > one. If all that you want is for abs(x) to automatically return x (or
> > something similar) it suffices to define x as `x=Symbol('x',
> > positive=True)`. There are a few other handles like `real` and `integer`.
> >
> > - if you need something more general or more fancy, we may have it in
> some
> > (possibly unfinished, mostly unused) form, but it goes deeper in SymPy
> so a
> > more precise question will help us give you a more precise answer.
> >
> >
> > On 24 July 2013 13:10, Ben Lucato <[email protected]> wrote:
> >>
> >> We can represent domains on paper quite easily - for instance we can
> write
> >> x < 0, or alternatively x (epsilon symbol) R-, or even x (epsilon
> symbol)
> >> (-infinity, 0)
> >>
> >> I looked around but couldn't really find that - is there a canonical way
> >> to be writing domains in SymPy?
> >>
> >> --
> >> You received this message because you are subscribed to the Google
> Groups
> >> "sympy" 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/sympy.
> >> For more options, visit https://groups.google.com/groups/opt_out.
> >>
> >>
> >
> >
> > --
> > You received this message because you are subscribed to the Google Groups
> > "sympy" 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/sympy.
> > For more options, visit https://groups.google.com/groups/opt_out.
> >
> >
>
> --
> You received this message because you are subscribed to a topic in the
> Google Groups "sympy" group.
> To unsubscribe from this topic, visit
> https://groups.google.com/d/topic/sympy/vMa2TEbdb-k/unsubscribe.
> To unsubscribe from this group and all its topics, 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/sympy.
> For more options, visit https://groups.google.com/groups/opt_out.
>
>
>
--
Ben Lucato
----------------------------------------------------------------------------------
Phone: +61 400 159 632 | Email: [email protected]
--
You received this message because you are subscribed to the Google Groups
"sympy" 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/sympy.
For more options, visit https://groups.google.com/groups/opt_out.
