Fix display of tensors on free modules of finite rank

[egourgoulhon]

The following is a bug:

sage: M = FiniteRankFreeModule(SR, 3, name='M')
sage: e = M.basis('e')
sage: t = SR.var('t', domain='real')
sage: (2*e[0]).display()
2 e_0
sage: (t*e[0]).display()
0

The outcome of the last line should be t e_0. This bug arises because of the nonzero check performed to avoid displaying zero components. This check is written as t != 0, which returns False. The fix proposed in this ticket is to replace it by not (t==0), which returns True.

CC: @tscrim

Component: linear algebra

Keywords: tensor

Author: Eric Gourgoulhon

Branch/Commit: 7c02ed8

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/22520

[egourgoulhon]

New commits:

7c02ed8

Fix display of tensors on free modules of finite rank (#22520)

[egourgoulhon]

Branch: public/manifolds/bug-display-tensor-22520

[egourgoulhon]

Commit: 7c02ed8

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:2

It's somewhat ugly, but a necessary evil because of how symbolic works (i.e., t could be 0).

[egourgoulhon]

comment:3

Replying to @tscrim:

It's somewhat ugly, but a necessary evil because of how symbolic works (i.e., t could be 0).

I agree.
Thanks for the review!

[vbraun]

Changed branch from public/manifolds/bug-display-tensor-22520 to 7c02ed8