add a free_variables() method?

[sagetrac-wonder]

It can be useful to query the free variables in an expression. SR's variables() and arguments() return all variables in an expression, whether free or bound. For example:

sage: var('y')
y
sage: function('f')
f
sage: e = limit( f(x,y), x=0 )
sage: e
limit(f(x, y), x, 0)
sage: e.variables()
(x, y)

I would like to have a free_variables() method that returns only y in this case. Is there a recommended way to get this information from an expression?

Depends on #22844
Depends on #23134

CC: @EmmanuelCharpentier

Component: symbolics

Author: Ralf Stephan

Branch/Commit: 5b93a06

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/20179

[rwst]

comment:1

These are practically all variables, minus the one(s) the limit is over?

[sagetrac-wonder]

comment:2

The free variables in an expression are all its variables excluding any that are bound, for example, in limits, sums, products, or integrals.

See for example https://en.wikipedia.org/wiki/Free_variables_and_bound_variables for a definition.

[rwst]

comment:3

Implemented in pynac git master. Will be in the upcoming Pynac-0.7.6.

[rwst]

Branch: u/rws/add_a_free_variables___method_

[rwst]

comment:5

This is not ready for review because it doesn't work as expected but at least the interface is there now.

---

New commits:

3c848da	22838: pkg version/checksum
d89e6d0	22838: remove unnecessary patch
4a30119	22838: interface change
7d3fd60	22838: doctest adaptation to ticket 10070
5b93a06	20179: interface to Pynac's ex::free_symbols()

[rwst]

Commit: 5b93a06

[rwst]

Author: Ralf Stephan

[rwst]

Dependencies: #22844

[rwst]

Changed dependencies from #22844 to #22844, pynac-0.7.8

[rwst]

comment:8

The problems seem resolved, now that there is a symbolic limit, and code in Pynac master that recognizes it and its bound symbols.

[rwst]

Changed dependencies from #22844, pynac-0.7.8 to #22844, #23134

[tscrim]

comment:10

Is this ready for review? If so, then you can set it to positive review on my behalf.

[tscrim]

Reviewer: Travis Scrimshaw

[rwst]

comment:11

Yes, I usually wait until the merge of the Pynac upgrade because not all reviewers want to go through the hassle of manual Pynac install. Thanks.

[vbraun]

Changed branch from u/rws/add_a_free_variables___method_ to 5b93a06