expand() only expands the denominator when it gets the deep=True flag (because
it is inside a Pow, namely, -1). So I guess factor needs to know to use that
flag when it gets frac=True.
The last item is a printing issue, and has nothing to do with factor or expand.
Aaron Meurer
On May 27, 2010, at 3:49 PM, smichr wrote:
> Is the following behavior correct for factor?
>
>>>> from sympy import *
>>>> var('x y')
> (x, y)
>>>> eq = x*(1+2*y+y**2)+1+2*y+y**2
>
> Here we show what happens with and without expand being set:
>>>> factor(eq,expand=0)
> 1 + 2*y + x*(1 + 2*y + y**2) + y**2
>>>> factor(eq,expand=1)
> (1 + y)**2*(1 + x)
>
> Now try the same when eq is in the denominator:
>>>> factor(1/eq,expand=0,frac=1)
> 1/((1 + x)*(1 + y)**2)
>>>> factor(1/eq,expand=1,frac=1)
> 1/((1 + x)*(1 + y)**2)
>
> I would have expected that expand=0 with frac=1 would have given
> 1/(1 + 2*y + x*(1 + 2*y + y**2) + y**2)
>
> Also why are the terms reversed in the numerator and denominator?
>
>>>> factor(eq,expand=1)
> (1 + y)**2*(1 + x)
>>>> factor(1/eq,expand=1,frac=1)
> 1/((1 + x)*(1 + y)**2)
>
> (Notice that 1+x is changing positions.)
>
> This behavior was also tested in polys9.
>
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