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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