On logarithm of a powerseries

[Zhibin Liang]

Dear all,

Assume that f is a power series, how to calculate the power series of log(f)?


Very best wishes
Zhibin Liang

[David Roe]

Use log(1-f) = -f - f^2/2 - f^3/3 + .... from integrating the identity
1/(1-x) = 1 + x + x^2 + ....
David

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[Zhibin Liang]

Thank you. However, I really want a non-trivial function.

2011/10/3 David Roe <ro...@math.harvard.edu>

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Very best wishes
Zhibin Liang

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[daveloeffler]

On Oct 3, 8:31 am, Zhibin Liang <liang...@gmail.com> wrote:
> Thank you. However, I really want a non-trivial function.

Dear Liang,

I'm not sure what you mean by "non-trivial"? I guess you mean that you
want to be able to type "log(f)" and have it just work, in the same
way "exp(f)" does. To write such a function would be very easy, at
least when the constant term is 1 or the base ring of the power series
ring already has log implemented. You should open a ticket on the Sage
trac server (trac.sagemath.org).

David