Hi Urs,
On 21 Okt., 11:35, Urs Hackstein <[email protected]> wrote:
> Well, the definition of f contains a lot of symbolic variables, so that
> might be the problem. I don't define f at once, but succesively. Starting
> with the fraction
>
> T12*T22*Z21*Z22/T1*T2*Z21+T1*T2*Z22,
>
> I replace successively all symbolic variables by expressions with new
> siymbolic variables, so that f grows larger and larger.
So, in a nutshell, you do things like
sage: var('T1 T2')
(T1, T2)
sage: P.<s> = CC[]
sage: q = T1/T2
sage: p = q.subs(T1=1,T2=s)
sage: p.parent()
Symbolic Ring
Not good. I would have expected it to end up in the quotient ring of
P. Also, it won't help to define q as a symbolic function and evaluate
T1 and T2:
sage: q(T1,T2) = T1/T2
sage: p = q(T1=1,T2=s)
sage: p.parent()
Symbolic Ring
Of course, as Maarten has pointed out, you can explicitly cast p into
the fraction field of P:
sage: F = Frac(P)
sage: F(p).parent()
Fraction Field of Univariate Polynomial Ring in s over Complex Field
with 53 bits of precision
sage: F(p)
1.00000000000000/s
Or, which may both be easier and faster, you could define an actual
Python function that returns an arithmetic expression out of input
data T1,T2,T3,...:
sage: def q(T1,T2):
....: return T1/T2
....:
sage: p = q(1,s)
sage: p.parent()
Fraction Field of Univariate Polynomial Ring in s over Complex Field
with 53 bits of precision
Best regards,
Simon
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