[Maxima-bugs] [ maxima-Bugs-1624975 ] Bug in AntiDifference (Maxima 5.11.0)

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Bugs item #1624975, was opened at 2006-12-30 09:55
Message generated for change (Settings changed) made by robert_dodier
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>Category: Share Libraries
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Nobody/Anonymous (nobody)
>Assigned to: Andrej Vodopivec (andrejv)
Summary: Bug in AntiDifference (Maxima 5.11.0)

Initial Comment:
(%i1) display2d:false;

(%o1) false
(%i2) load(zeilberger);

(%o2)
?\/usr\/share\/maxima\/5\.11\.0\/share\/contrib\/Zeilberger\/zeilberger\.mac
(%i3) AntiDifference(-(1/(n+1)-1/n),n);

(%o3) (-n-1)*(1/n-1/(n+1))
(%i4) AntiDifference((1/(n+1)-1/n),n);

Unknown operator :  -
1/(n+1)-1/n  is not hypergeometric in  n
(%o4) NON_HYPERGEOMETRIC



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>Comment By: Robert Dodier (robert_dodier)
Date: 2007-01-08 19:54

Message:
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user_id=501686
Originator: NO

Assigning this item to Andrej V since he seems to be working on some bug
fixes for zeilberger.

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Comment By: Nobody/Anonymous (nobody)
Date: 2007-01-07 03:22

Message:
Logged In: NO 

This fix does not work but Andrej found the right one. Add another
(recursive) else if at the end of shiftQuoHypCheckAux:

       else if op(expr)="-" then 
               return(shiftQuoHypCheckAux(-expr, k, hyp_flag))
       
Explanation: we are computing the shiftquotient f(k+1)/f(k). So an initial
unary minus is irrelevant.
Therefore we just drop it.
 

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Comment By: Nobody/Anonymous (nobody)
Date: 2007-01-06 13:47

Message:
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Blindly changing

if op(expr) = "+"  then

into

if op(expr) = "+"  or op(expr)="-" then

near the end of the function

shiftQuoHypCheckAux(expr,k,hyp_flag)

in zeilberger/shiftQuotient.mac

seems to fix this bug.

I didn't do much testing. Are there any regression tests around for
zeilberger?



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Comment By: Nobody/Anonymous (nobody)
Date: 2007-01-06 10:43

Message:
Logged In: NO 

Blindly changing

if op(expr) = "+"  then

into

if op(expr) = "+"  or op(expr)="-" then

near the end of the function

shiftQuoHypCheckAux(expr,k,hyp_flag)

in zeilberger/shiftQuotient.mac

seems to fix this bug.

I didn't do much testing. Are there any regression tests around for
zeilberger?



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Comment By: Nobody/Anonymous (nobody)
Date: 2007-01-06 10:29

Message:
Logged In: NO 

This bug is probably easy to fix. The error message comes from
the fuction shiftQuoHypCheckAux in the file
zeilberger/shiftQuotient.mac. This checks for
all possible operators in a certain expression and does something. It
checks for "+"
but forgets to check for "-". Somebody who is slightly familiar with the
Gosper algorithm can
probably figure out how to correct this.



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