inconsistency for variables method, leads to errors in differentiation

[robertwb]

Hi William:

I was running Sage 3.0.2 on Linux when the error occurred.  Just now i
upgraded to 'sage-3.0.6-i686-Linux-debian-intel' without problems, ran
the same code (in a notebook and on the command line), and got the
same error.  Hmm, i don't understand why Sage can do 'diff(f*SR(2),x)'
but not 'diff(f*SR(1),x)'.

Alex

This boils down to the fact that some symbolic objects take an extra argument in their variables method. It is unclear what the meaning of this argument is (couldn't find any examples) and if it should be removed, or added, to make things consistent. (I'd guess removed, but I don't want to break things.)

Component: calculus

Issue created by migration from https://trac.sagemath.org/ticket/3779

[garyfurnish]

comment:1

The argument doesn't exist in symbolics, so I'm in favor of removal (and I have no idea what it does either)

[mwhansen]

comment:2

The argument was used to pass in additional variables to the variables method which would then be subsequently returned. This functionality was never used, and I can't / couldn't think of a case where it would be needed. So, I do think the correct fix is to remove it. I've attached a patch which does that and passes tests.

[robertwb]

comment:3

Attachment: trac_3779.patch.gz

Looks good to me, and fixes the bug. The only question I had is why you wrote tuple([]) rather than (), but I'm OK with that.

[mwhansen]

comment:4

There's no real reason -- it's just what I happened to type :-)

[mwhansen]

Attachment: trac_3779-2.patch.gz

[sagetrac-mabshoff]

comment:5

Merged both patches in Sage 3.1.alpha1