Hi Francesc,
On Wed, Aug 6, 2014 at 2:24 PM, Francesc Ferrer
<[email protected]> wrote:
> Hello,
>
> Repeated calls to 'coeff' give inconsistent results:
>
> import sympy
>
> x, y, a, b = sympy.symbols( 'x y a b')
>
> f = a*x**2*y**2 + b*x*y**2
>
> Then, the commands 'f.coeff(x,2).coeff(y,2)' and 'f.coeff(y,2).coeff(x,2)'
> both give 'a', which is correct.
>
> The command f.coeff(y,0).coeff(x,2) gives 0 as expected.
>
> However, f.coeff(x,2).coeff(y,0) gives 'a', which is wrong!
>
> Is this a bug, or am I missing something obvious?
Which sympy version are you using? I just tried a recent git version
(49bf47d24e3bcbe3e7d16e6bf08216ab1976f410) and I can't reproduce the
behavior
you described:
In [1]: var("x y a b")
Out[1]: (x, y, a, b)
In [2]: f = a*x**2*y**2 + b*x*y**2
In [3]: f
Out[3]:
2 2 2
a⋅x ⋅y + b⋅x⋅y
In [4]: f.coeff(x, 2)
Out[4]:
2
a⋅y
In [5]: f.coeff(x, 2).coeff(y, 2)
Out[5]: a
In [6]: f.coeff(x, 2).coeff(y, 0)
Out[6]: 0
Ondrej
>
> -Francesc
>
>
>
>
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