Return index of variable

515 ●9 ●20 ●38

I have the following

R.<a> = InfinitePolynomialRing(QQ)
b = a[3]    # 3 or any arbitrary non-negative integer

Is there a function that takes b as the input and gives the 3 back?

Emmanuel Charpentier
7774 ●6 ●51 ●154

This seems to work :

sage: R1.<a>=InfinitePolynomialRing(QQ)
sage: reset()
sage: R1.<a>=InfinitePolynomialRing(QQ)
sage: b=a[3]
sage: R1.varname_key(str(b))[1]
3

See R1.varname_key? for further enlightment... ;-)

HTH,

Comments

Thanks! Do you know how I can get the degree back, for example: p = a[1]*a[2]^2, but p.degree(a[1]) doesn't work.

Thrash ( 2022-11-19 00:00:18 +0100 )edit

OK, I found it, it's p.degree(a[1].variable()).

Thrash ( 2022-11-19 00:12:25 +0100 )edit

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