[Maxima-bugs] [ maxima-Bugs-3438735 ] sublis into indeterminate

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Bugs item #3438735, was opened at 2011-11-16 03:37
Message generated for change (Comment added) made by crategus
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Barton Willis (willisbl)
Assigned to: Nobody/Anonymous (nobody)
Summary: sublis  into indeterminate

Initial Comment:
(%i10) q : x*cos(x)/sin(x);
(%o10) (x*cos(x))/sin(x)

(%i11) sublis([x=0],q);
(%o11) 0



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>Comment By: Dieter Kaiser (crategus)
Date: 2011-11-16 10:56

Message:
The reason is the way of simplification of zeros in simptimes:

(%i1) q : x*cos(x)/sin(x)$

(%i2) :lisp (trace simptimes)
(SIMPTIMES)

(%i2) sublis([x=0], q);
  0: (SIMPTIMES ((MTIMES) 0 ((%COS) 0) ((MEXPT) ((%SIN) 0) -1)) 1 NIL)
  0: SIMPTIMES returned 0
(%o2) 0

If simptimes recognizes  a zero as a factor, it returns immediately without
further examination of the other factors. This behavior can be seen in a
simple example:

This is the expected result:

(%i3) 0.0*0;
(%o3) 0.0

But this not. The type of the expression is not recognized. simptimes
returns after the first occurrence of the value zero.

(%i3) 0*0.0;
(%o3) 0

Dieter Kaiser

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