[Maxima-bugs] [ maxima-Bugs-2555600 ] substitution into conditional

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Bugs item #2555600, was opened at 2009-02-01 05:50
Message generated for change (Comment added) made by robert_dodier
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>Category: Lisp Core
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Barton Willis (willisbl)
Assigned to: Nobody/Anonymous (nobody)
Summary: substitution into conditional

Initial Comment:
(%i5) subst(x = 0, '(if x < 1 then 5 else log(x)));
log(0) has been generated.

 

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>Comment By: Robert Dodier (robert_dodier)
Date: 2009-03-03 21:57

Message:
Well, I think subst is just incidental here.

There are actually a couple of interacting problems here.
(1) Should branches of conditionals be simplified when the conditional
expression is simplified?
(2) Should errors be triggered in simplification?

At present branches of conditionals are simplified, and errors are
triggered in simplification (e.g. 1/0, log(0), gamma(0)). 

Either (1) or (2) or both could go the other way. My own preference is for
(1) but not (2), i.e. continue to simplify branches, and prohibit errors in
simplification.

Given the current policies (1) and (2), the observed behavior is to be
expected; I guess it's a misfeature but I don't know if it's accurate to
call it a bug.

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