Fix usage of symbolic comparison in several places

[rwst]

Symbolic comparison is wrongly used in several places throughout Sage (overview https://trac.sagemath.org/wiki/symbolics/nonzero). The ticket replaces code involuntarily calling __nonzero__ with a call of the is_zero or is_equal member functions to clarify if simplification is needed or not. The code positions calling __nonzero__ were obtained by raising an exception in __nonzero__ and analyzing the resulting doctest fails. Of course not every simplification is unwanted so every case must be considered and tested.

CC: @cheuberg @dkrenn

Component: performance

Author: Ralf Stephan

Branch/Commit: u/rws/fix_usage_of_symbolic_comparison_in_several_places @ d08957e

Issue created by migration from https://trac.sagemath.org/ticket/24992

[rwst]

Description changed:

--- 
+++ 
@@ -1,3 +1,3 @@
-Symbolic comparison is wrongly used in several place throughout Sage (overview https://trac.sagemath.org/wiki/symbolics/nonzero). The ticket replaces code involuntarly calling `__nonzero__` with a call of the `is_zero` member function to clarify if simplification is needed or not.
+Symbolic comparison is wrongly used in several places throughout Sage (overview https://trac.sagemath.org/wiki/symbolics/nonzero). The ticket replaces code involuntarily calling `__nonzero__` with a call of the `is_zero` and `is_equal` member functions to clarify if simplification is needed or not.
 
 Resulting speedups will not be surprising.

[rwst]

Description changed:

--- 
+++ 
@@ -1,3 +1 @@
-Symbolic comparison is wrongly used in several places throughout Sage (overview https://trac.sagemath.org/wiki/symbolics/nonzero). The ticket replaces code involuntarily calling `__nonzero__` with a call of the `is_zero` and `is_equal` member functions to clarify if simplification is needed or not.
-
-Resulting speedups will not be surprising.
+Symbolic comparison is wrongly used in several places throughout Sage (overview https://trac.sagemath.org/wiki/symbolics/nonzero). The ticket replaces code involuntarily calling `__nonzero__` with a call of the `is_zero` or `is_equal` member functions to clarify if simplification is needed or not. The code positions calling `__nonzero__` were obtained by raising an exception in `__nonzero__` and analyzing the resulting doctest fails. Of course not every simplification is unwanted so every case must be considered and tested.

[rwst]

Branch: u/rws/fix_usage_of_symbolic_comparison_in_several_places

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

e1942d0

24992: fixes

[sagetrac-git]

Commit: e1942d0

[rwst]

comment:5

I get a 10-15% decrease of CPU time with this branch when doing sage -tp src/sage/rings/asymptotic/ (from 31.5s to 26.5-28.5s).

It's not finished, there are more instances in Sage where the changes can be applied.

[sagetrac-git]

Changed commit from e1942d0 to d08957e

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

d08957e

24992: more optimizations

[rwst]

Author: Ralf Stephan