A bug in simplify_rational() function?

asked 2017-11-26 13:35:08 +0100

When I run the following

var('z')
( 1/z + 1/z.conjugate() ).simplify_rational()

on sage-8.0 / Ubuntu 16.04 LTS, I get the following answer, which is evidently wrong.

2/z

Can anyone explain why this phenomenon happens? It it a bug in simplify_rational() function?

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Comments

The following dialog with the sage interpreter may highlight the implicit assumption:

sage: var('z')
z
sage: ( 1/z + 1/z.conjugate() ).simplify_rational()
2/z
sage: assume( z, 'complex' )
sage: ( 1/z + 1/z.conjugate() ).simplify_rational()
(z + conjugate(z))/(z*conjugate(z))
sage: ?assume
sage: forget()
sage: ( 1/z + 1/z.conjugate() ).simplify_rational()
2/z