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

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Bugs item #891338, was opened at 2004-02-05 13:10
Message generated for change (Comment added) made by pfarner
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105083&aid=891338&group_id=5083

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&#039;ll keep looking into this, to nail down exactly
what&#039;s happening.
Perhaps some rules don&#039;t interact well, or a rule
should be added.
This might also be related to the fact that the
function isn&#039;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&#039;ll want it
to report that problem cleanly, so this is a bug.

As I said, I&#039;m researching this one, but I&#039;m also
reporting it as a
matter of proper practice.


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>Comment By: Preston Pfarner (pfarner)
Date: 2004-04-03 09:38

Message:
Logged In: YES 
user_id=945156

Yes, I am working on HartMath some, but I've been idle for
the last couple of weeks because I was on vacation.  It's
possible that it makes more sense to put effort into hmath
(hmath.org), a possible successor. *shrug*

On this bug, I've found that at some point in the process of
evaluating a derivative (even D(x,x)) the rules for Sin()
appear to be put into List().  I don't know how this is
happening, but it's definitely not good.  This is obviously
wrong, and I haven't tracked it down yet.

For another example, if I evaluate List(Multiply(1/4,Pi)) on
its own, I get no simplification.  If I do it after a
derivative has been evaluated, I get
List(Multiply(1/4,Pi))=1.  Naturally, this would be true if
the "List" were "Sin", but somewhere in there the wrong
rules are being loaded.  I have some more introspection to
add, and then it'll probably become clear (and be fixed).

While the dynamic on-the-fly loading of capabilities is nice
for latency (start-up speed) reasons, it can defer bugs like
this until some condition occurs, making them harder to find.

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Comment By: Scott Lett (slett)
Date: 2004-04-03 09:26

Message:
Logged In: YES 
user_id=49890

Preston, does this mean that you're working on Hartmath 
now?

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You can respond by visiting: 
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