Absolute value function for scalar fields

[mjungmath]

Currently, the abs operator cannot be applied to scalar fields:

sage: M = Manifold(2, 'M', structure='topological')
sage: X.<x,y> = M.chart()
sage: f = M.scalar_field({X: x*y}, name='f', latex_name=r"\Phi")
sage: abs(f)
Traceback (most recent call last)
...
TypeError: bad operand type for abs(): 'ScalarFieldAlgebra_with_category.element_class'

In this ticket, we add this feature.

CC: @egourgoulhon @tscrim

Component: manifolds

Author: Michael Jung

Branch/Commit: 2095de3

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/32396

[mjungmath]

Branch: u/gh-mjungmath/abs_function_for_scalar_fields

[mjungmath]

Commit: fcd64c9

[mjungmath]

New commits:

fcd64c9

Trac #32396: add `__abs__` to chart_func and scalarfield

[mjungmath]

Description changed:

--- 
+++ 
@@ -1,10 +1,10 @@
 Currently, the `abs` operator cannot be applied to scalar fields:
 
 ```
-sage:             sage: M = Manifold(2, 'M', structure='topological')
-....:             sage: X.<x,y> = M.chart()
-....:             sage: f = M.scalar_field({X: x*y}, name='f', latex_name=r"\Phi")
-....: abs(f)
+sage: M = Manifold(2, 'M', structure='topological')
+....: X.<x,y> = M.chart()
+....: f = M.scalar_field({X: x*y}, name='f', latex_name=r"\Phi")
+sage: abs(f)
 Traceback (most recent call last)
 ...
 TypeError: bad operand type for abs(): 'ScalarFieldAlgebra_with_category.element_class'

[mjungmath]

Description changed:

--- 
+++ 
@@ -2,8 +2,8 @@
 
 ```
 sage: M = Manifold(2, 'M', structure='topological')
-....: X.<x,y> = M.chart()
-....: f = M.scalar_field({X: x*y}, name='f', latex_name=r"\Phi")
+sage: X.<x,y> = M.chart()
+sage: f = M.scalar_field({X: x*y}, name='f', latex_name=r"\Phi")
 sage: abs(f)
 Traceback (most recent call last)
 ...

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:5

LGTM.

[mjungmath]

comment:6

Thank you for the review!