missing log attribute for power series

[fchapoton]

Consider the following

sage: x=PowerSeriesRing(QQ,'x').gen()
sage: x.exp()                        
1 + x + 1/2*x^2 + 1/6*x^3 + 1/24*x^4 + 1/120*x^5 + 1/720*x^6 + 1/5040*x^7 + 1/40320*x^8 + 1/362880*x^9 + 1/3628800*x^10 + 1/39916800*x^11 + 1/479001600*x^12 + 1/6227020800*x^13 + 1/87178291200*x^14 + 1/1307674368000*x^15 + 1/20922789888000*x^16 + 1/355687428096000*x^17 + 1/6402373705728000*x^18 + 1/121645100408832000*x^19 + O(x^20)
sage: x.log()
AttributeError                            Traceback (most recent call last)
...
AttributeError: 'sage.rings.power_series_poly.PowerSeries_poly' object has no attribute 'log'

I think it would be good to have log if one has exp, in order to be able to go back and forth. Of course, one should check that the constant term is 1.

Here is a patch that does the job.

Component: algebra

Keywords: logarithm, power series, days45

Author: Frédéric Chapoton

Reviewer: Travis Scrimshaw

Merged: sage-5.8.beta0

Issue created by migration from https://trac.sagemath.org/ticket/14115

[fchapoton]

Attachment: trac_14115-fc.patch.gz

[fchapoton]

Author: Frédéric Chapoton

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

Changed keywords from logarithm, power series to logarithm, power series, days45

[tscrim]

comment:3

Attachment: trac_14155-review-ts.patch.gz

Hey Frederic,

Looks good. I've uploaded a small review patch which tweaks the documentation. If you agree with my changes, go ahead and set this to positive review.

Best,

Travis

[fchapoton]

comment:4

ok, then positive review

[jdemeyer]

Merged: sage-5.8.beta0