Hi,
On 27 May 2011 06:31, Aaron S. Meurer <asmeu...@gmail.com> wrote:
> Well, it still fails there with the subs. Like I said, it's a bug. Can
> you open an issue for it?
>
It's not necessarily a bug, because you expect subs() (sympy) and findroot()
(mpmath) to work together, but you are skipping the glue (core/evalf.py or
wherever this is). I'm not sure how exactly evalf code in SymPy works, but I
think that manipulation of mp.dps (or .prec) doesn't affect evalf (the
reason to think this way is that each instance of mpf can have its own
dps/prec setting). Poly.eval (also nroots()) work because it uses mpf
directly, skipping the glue.
>
> Aaron Meurer
>
> On May 26, 2011, at 9:09 PM, Matthew Emmett wrote:
>
> > Thanks for the quick reply Aaron. I will get the latest git version
> > and run with it. BTW, I was running the sample on 0.6.7.
> >
> > Thanks again,
> > Matt
> >
> > On Thu, May 26, 2011 at 08:28:51PM -0600, Aaron S. Meurer wrote:
> >> If I try this with mpmath 0.16 (the version we currently have in sympy
> in the latest git master), I get:
> >>
> >> In [22]: print 'subs: ', mpmath.findroot(lambda xi: p.subs(x, xi), 1.0)
> >> subs:
> ---------------------------------------------------------------------------
> >> ValueError Traceback (most recent call
> last)
> >>
> >> /Users/aaronmeurer/Documents/python/sympy/sympy/<ipython console> in
> <module>()
> >>
> >>
> /Users/aaronmeurer/Documents/python/sympy/sympy/sympy/mpmath/calculus/optimization.pyc
> in findroot(ctx, f, x0, solver, tol, verbose, verify, **kwargs)
> >> 968 '(%g > %g)\n'
> >> 969 'Try another starting point or tweak
> arguments.'
> >> --> 970 % (norm(f(*xl))**2, tol))
> >> 971 return x
> >> 972 finally:
> >>
> >> ValueError: Could not find root within given tolerance. (6.67917e-33 >
> 1.71057e-49)
> >> Try another starting point or tweak arguments.
> >>
> >> Another option for Poly is eval. I get this:
> >>
> >> In [37]: print 'eval: ', mpmath.findroot(lambda xi: p.eval(x, xi), 1.0)
> >> eval: 0.774596669241483377035853079956479922166584341
> >>
> >> In [38]: print 'exact: ',
> mpmath.sqrt(mpmath.mpf('3.0')/mpmath.mpf('5.0'))
> >> exact: 0.774596669241483377035853079956479922166584341
> >>
> >> In [39]: print 'lambda:', mpmath.findroot(lambda x: 5.0*x**3/2.0 -
> 3.0*x/2.0, 1.0)
> >> lambda: 0.774596669241483377035853079956479922166584341
> >>
> >> So I'd say there is some kind of bug with subs.
> >>
> >> Aaron Meurer
> >>
> >> On May 26, 2011, at 8:21 PM, Matthew Emmett wrote:
> >>
> >>> Hi everyone,
> >>>
> >>> I am having trouble combining mpmath's findroot function with sympy.
> >>> Here is a short example of what I am trying to accomplish:
> >>>
> >>> import sympy
> >>> import mpmath
> >>>
> >>> mpmath.mp.dps = 45
> >>>
> >>> x = sympy.var('x')
> >>> p = (5.0/2.0*x**3 - 3.0/2.0*x).as_poly()
> >>>
> >>> print 'subs: ', mpmath.findroot(lambda xi: p.subs(x, xi), 1.0)
> >>> print 'lambda:', mpmath.findroot(lambda x: 5.0*x**3/2.0 - 3.0*x/2.0,
> >>> 1.0)
> >>> print 'exact: ', mpmath.sqrt(mpmath.mpf('3.0')/mpmath.mpf('5.0'))
> >>>
> >>>
> >>> The output is:
> >>>
> >>> subs: 0.77459666924148342341315597798728447146706553
> >>> lambda: 0.774596669241483377035853079956479922166584341
> >>> exact: 0.774596669241483377035853079956479922166584341
> >>>
> >>>
> >>> That is, when using mpmath.findroot, substituting into a SymPy
> >>> polynomial does not produce the same result as using a lambda form
> >>> with a handwritten version of the polynomial. Is there a way to the
> >>> SymPy subs method to work as expected?
> >>>
> >>> Thanks,
> >>> Matt
> >>>
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Mateusz
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