Hi,
On 16 April 2010 13:03, Ben Goodrich <goodrich....@gmail.com> wrote:
> Hi Mateusz
>
> On Apr 16, 11:46 am, Mateusz Paprocki <matt...@gmail.com> wrote:
> > SymPy can compute things like F*G - H**2 fast, unfortunately not on the
> > user level. Below you will find a short tutorial how to do it fast but
> > messy way.
> >
> > Lets assume you have polynomial-like expressions F, G, H. For my own
> > convenience, when experimenting, I made my self a function fun() which
> > returns those expressions:
> >
> > In [1]: %time F, G, H, gens = fun()
> > CPU times: user 12.03 s, sys: 0.00 s, total: 12.03 s
> > Wall time: 12.46 s
>
> What exactly is gens here? I thought it was supposed to be a list that
> contains all the symbols in the polynomials, but then I eventually run
> into this error
>
> /tmp/mattpap-sympy-polys-cd30a32/sympy/polys/polytools.py in
> _init_poly_from_list(list_rep, *gens, **args)
> 286
> 287 if len(gens) != 1:
> --> 288 raise PolynomialError("can't create a multivariate
> polynomial from a list")
>
>
gens is just a list of symbols. The error tells you that you can't create
multivariate polynomials using nested lists. Use dictionaries instead. E.g.:
Poly([1,2,3], x) is ok, but not Poly([[1],[2],[3]], x, y), use Poly({(2,0):
1, (1,0): 2, (0,0): 3}, x, y).
>
> Thanks,
> Ben
>
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>
Mateusz
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