On Nov 27, 2007 11:11 PM, kent-and <[EMAIL PROTECTED]> wrote:
>
>
> > So you want:
> >
> > In [4]: f = x+y
> >
> > In [5]: g = x+z
> >
> > In [6]: f*g
> > Out[6]: (x + y)*(x + z)
> >
> > In [7]: f+g
> > Out[7]: y + z + 2*x
> >
> > So [6] is ok, but you want [7] to be "x+y+x+z" instead? Is it because
> > of memory requirements (see that issue for more details)?
> >
> >
>
> Well something like this, let say
>
> f = pow(x+1, 12) + pow(x-1, 12)
>
> This is a very efficient representation of f in terms of the number of
> operations
> needed to evaluate f(x). Once expanded it is not easy to go back to
> an
> efficient representation without knowing what f was.
But I think both ginac and SymPy work in this way already:
In [1]: (x+1)**12 + (x-1)**12
Out[1]:
12 12
(1 + x) + (1 - x)
In [2]: f = (x+1)**12 + (x-1)**12
In [3]: f
Out[3]:
12 12
(1 + x) + (1 - x)
In [4]: f.expand()
Out[4]:
12 2 10 4 8 6
2 + 2*x + 132*x + 132*x + 990*x + 990*x + 1848*x
SymPy's automatic evaluation works in a way to only simplify things,
that can be done in a very fast way. Expanding doesn't belong to that
categhory.
> BTW: I've tested the patch, great speed-up, great work!
Thanks! It will be committed and released soon.
Ondrej
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