2011/12/7 Ondřej Čertík <ondrej.cer...@gmail.com> > On Wed, Dec 7, 2011 at 11:58 AM, Ronan Lamy <ronan.l...@gmail.com> wrote: > > Le mercredi 07 décembre 2011 à 20:36 +0100, krastanov.ste...@gmail.com 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()? Is it plausible in the meantime to have (is_something or ask(..))? Of course in some cases 'or' wont be the correct operator.
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