Here is some code that I think will do the trick.
sage: def subexpressions(e):
....: res = []
....: if not hasattr(e, '_operands'):
....: return []
....: for op in e._operands:
....: res.append(op)
....: res += subexpressions(op)
....: return res
....:
sage: e = exp(x)+1
sage: f = exp(x)
sage: subexpressions(e)
[e^x, exp, x, 1]
sage: f in subexpressions(e)
True
--Mike
On 10/1/07, Ondrej Certik <[EMAIL PROTECTED]> wrote:
>
> Hi,
>
> I was curious, so I started to port the algorithm. Now I have this problem:
>
> sage: e = exp(x)+1
> sage: f = exp(x)
>
> I need to check, that f is a subexpression of e. In SymPy, I do:
>
> e.subs(f, Symbol("x", dummy=True))==e
>
> i.e. I substitute f for some dummy variable and compare if the
> expression has changed. If it did, f is a subexpression of e. In SAGE
> however, is there a way how to substitute the whole exp(x) in the
> expression (exp(x)+1) by something else?
>
> Thanks,
> Ondrej
>
> >
>
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