Log of integer to base 1/n can have exact numeric results

[rwst]

Log of integer to base 1/n can have nonsymbolic results but this is not recognized in Integer::log():

sage: ZZ(8).log(1/2)
log(8)/log(1/2)

nor in Integer.exact_log():

sage: ZZ(8).exact_log(1/2)
...
TypeError: no conversion of this rational to integer

Component: numerical

Author: Ralf Stephan

Branch/Commit: 4aba8a9

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/21517

[rwst]

Branch: u/rws/log_of_integer_to_base_1_n_can_have_exact_numeric_results

[rwst]

Author: Ralf Stephan

[rwst]

Commit: 0ae5fd8

[sagetrac-git]

Changed commit from 0ae5fd8 to de1acfa

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

de1acfa

21517: handle ZZ.log(1/n)

[tscrim]

comment:4

I would avoid doing the exact_log twice:

        if type(m) == Integer and type(self) == Integer:
             elog = self.exact_log(m):
             if m**elog == self:
                 return elog

Similarly for the other one. Otherwise LGTM.

[tscrim]

Reviewer: Travis Scrimshaw

[sagetrac-git]

Changed commit from de1acfa to 4aba8a9

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

4aba8a9

21517: avoid duplicate computations

[rwst]

comment:7

Thanks.