On Wed, Dec 7, 2011 at 12:11 PM, [email protected] <[email protected]> wrote: > > > 2011/12/7 Ondřej Čertík <[email protected]> >> >> On Wed, Dec 7, 2011 at 11:58 AM, Ronan Lamy <[email protected]> wrote: >> > Le mercredi 07 décembre 2011 à 20:36 +0100, [email protected] a >> > écrit : >> >> How should assumptions be used? More precisely why the following code >> >> does what it does >> >> >> >> In [18]: global_assumptions.clear() >> >> >> >> In [19]: x = Symbol('x', positive=True) >> >> >> ^^^ This is old assumptions, that will be eventually removed >> >> >> >> >> In [20]: ask(Q.positive(x)) # Why does it return None? >> >> New assumptions. >> >> >> >> >> In [21]: x > 0 >> >> Out[21]: True >> >> Old assumptions. >> >> And so on. We need to write documentation how to use the new >> assumptions. I hit the same problems. Here is an example: >> >> + >>> from sympy import var, solve, S, refine, Q >> + >>> var("a z") >> + (a, z) >> + >>> f = z / (a**2+z**2)**(S(5)/2) >> + >>> solve(f.diff(z), z) >> + [-a/2, a/2] >> + >>> f.subs(z, a/2) >> + 16*sqrt(5)*a/(125*(a**2)**(5/2)) >> + >>> refine(f.subs(z, a/2), Q.positive(a)) >> + 16*sqrt(5)/(125*a**4) >> >> and we just need to document it well, then improve refine and other >> things, and then eventually remove the old assumptions. > > Does this mean that every instance of is_something must be changed to ask()?
Eventually yes, but from my talks with Mateusz at the Google Mentor Summit, unfortunately it is not easy to do it step by step, because for various technical reasons one will have to remove the old assumptions in one step (and fix some solvers that depend on it). > Is it plausible in the meantime to have (is_something or ask(..))? Of course > in some cases 'or' wont be the correct operator. I think it is currently completely independent, and we should simply start using the new assumptions. Ondrej -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
