[hartmath] [ hartmath-Bugs-891338 ] Stack Overflow from Infinite Recursion

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Bugs item #891338, was opened at 2004-02-05 13:10
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Category: None
Group: misc
Status: Open
Resolution: None
Priority: 5
Submitted By: Preston Pfarner (pfarner)
Assigned to: Nobody/Anonymous (nobody)
Summary: Stack Overflow from Infinite Recursion

Initial Comment:
I noticed that the attached simple test program fails
with a stack
overflow due to infinite recursion in the second EV() call.

Output:
  Before D(Pow(x,1/2),x)
  After  D(Pow(x,1/2),x)
  Before D(Pow(x,-1/2),x)
  Exception in thread "main" java.lang.StackOverflowError

When I run it with some extra instrumentation (printing
rules that are
applied, from HRuleSet.testDownRules()), I see that it
appears to be
applying the rule
{x_IsNumber}:=Check(SignumCmp(x)<0,I*Pi-{-x})
to List(1/2), then List(-1/2), and then repeating.

I'll keep looking into this, to nail down exactly
what's happening.
Perhaps some rules don't interact well, or a rule
should be added.
This might also be related to the fact that the
function isn't defined
for x<0, or that the second function has a pole (goes
to infinity)
at x=0.  However, even if the function behaves poorly,
we'll want it
to report that problem cleanly, so this is a bug.

As I said, I'm researching this one, but I'm also
reporting it as a
matter of proper practice.


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