On Oct 11, 10:24 pm, James Parson <par...@hood.edu> wrote:
> Dear sage-support,
>
> Is there a preferred built-in method for invoking elementary symmetric
> functions in Sage?
>
> The best that I could turn up was something like the following:
>
> sage: e = SFAElementary(QQ)
> sage: e([2]).expand(3)
> x0*x1 + x0*x2 + x1*x2
>
> That is very nice, but when I tried to automate some constructions (in
> Sage 4.5.3), I ran into the following sort of problem:
>
> sage: for i in range(3):
> ... print(e([i]).expand(3))
> Traceback (most recent call last):
> ...
> AttributeError: 'list' object has no attribute 'parent'
>
It turns out that Python starts counting at zero. So
sage: range(3)
[0, 1, 2]
So this works.
sage: for i in range(1,4):
e([i]).expand(3)
....:
x0 + x1 + x2
x0*x1 + x0*x2 + x1*x2
x0*x1*x2
For something a little more "Sage-ic", you could try
sage: for i in [1..3]:
e([i]).expand(3)
....:
x0 + x1 + x2
x0*x1 + x0*x2 + x1*x2
x0*x1*x2
This uses Sage Integers instead of Python ints.
However, none of this deals with the issue that the error message is
most uniformative for e([0]). Chalk this up as another place where
'empty' input causes some trouble. Someone on sage-combinat already
working on this particular instance (I know many of them have been
fixed recently)?
- kcrisman
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