But then, when I substitute positive symbol back to normal:
> symbols = f.free_symbols
> for symbol in symbols:
> f = f.subs(symbol, sympy.Symbol(symbol.name))
It still shows log(x), isntead of log(|x|)
On Wednesday, February 25, 2015 at 10:18:06 PM UTC+2, Joachim Durchholz
wrote:
>
> Am 25.02.2015 um 18:10 schrieb Paul Royik:
> > I mean in multithreaded environment, do people share same cache (and
> same
> > symbols)
> > If person1 created x=Symbol('x') and this is cached, and person2 created
> > x=Symbol('x', positive=True), do they have separate x's or they mixed,
> so
> > person1 can get positive x if it was overwritten in cache by person 2?
>
> If that's different persons (or, more precisely, shell sessions), they
> get different copies of the SymPy process anyway, and there's no
> confusion possible at all.
>
> > Reproduction.
> >
> > from sympy import *
> > x = Symbol('x')
> > f = log(x)
> > a=Wild('a')
> > symbols = f.free_symbols
> > for symbol in symbols:
> > f = f.subs(symbol, sympy.Symbol(symbol.name, positive=True))
> >
>
> Nit to pick: This wouldn't work for me, I'd have to do "import sympy"
> first.
>
> > print f.replace(log(a),log(Abs(a))) # prints log(x) as expected
> >
> > # clear_cache() solves the problem
> >
> > symbols = f.free_symbols
> > for symbol in symbols:
> > f = f.subs(symbol, sympy.Symbol(symbol.name))
> >
> > print f.replace(log(a),log(Abs(a))) # OOPS! prints log(x) instead of
> > log(|x|)
>
> Yes, that's happening for me, too, without any multithreading.
>
> It's okay though. You replaced that x in the original f==log(x) with a
> new x constructed as
>
> sympy.Symbol('x', positive=True)
>
> so you now have a new f, with an x that's already under an assumption
> that it must be positive.
> So I think what happens is that SymPy smartly infers that substituting
> an Abs(x) around an already-positive x is a nop and can be simplified out.
>
> Now I'd like to see a transcript of what happens with clear_cache().
> If my theory is correct, then clear_cache should not affect the outcome.
>
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