wrong symbolic sum

With CVS Maxima, the results are different:

 (%i18) sum(-k, k, -a, -1), simpsum, factor;
 (%o18) a*(a+1)/2

Manifestly empty sums simplify to zero:

 (%i19) sum(-k,k,5,-1);
 (%o19) 0

I suggest that we consider restoring the sumhack option.

Barton

-----maxima-bounces at math.utexas.edu wrote: -----

>To:?Alexandros?Droseltis?<ml-maxima at alex-droseltis.com>,?Maxima?List
><maxima at math.utexas.edu>
>From:?Richard?Fateman?<fateman at cs.berkeley.edu>
>Sent?by:?maxima-bounces at math.utexas.edu
>Date:?07/26/2009?09:09AM
>Subject:?Re:?[Maxima]?wrong?symbolic?sum
>
>Alexandros?Droseltis?wrote:
>>?Hello!
>>
>>?[Using?Maxima?5.17.0?provided?by?the?rpm?5.17.0-1.3?for?openSuSE]
>>
>>?Please,?have?a?look?at?this.
>>
>>?These?sums?are?correct:
>>
>>?(%i27)?sum(k,?k,?1,?4);
>>?(%o27)????????????????????????????????10
>>?(%i28)?sum(-k,?k,?-4,?-1);
>>?(%o28)????????????????????????????????10
>>
>>?Now?check?these?two?sums:
>>
>>?(%i1)?simpsum:?true;
>>?(%o1)????????????????????????????????true
>>?(%i2)?sum(k,?k,?1,?a);
>>??????????????????????????????????????2
>>?????????????????????????????????????a??+?a
>>?(%o2)???????????????????????????????------
>>???????????????????????????????????????2
>>?(%i3)?sum(-k,?k,?-a,?-1);
>>?Is??a??positive,?negative,?or?zero?
>>
>>?p;
>>??????????????????????????????????????2
>>?????????????????????????????????????a??-?a
>>?(%o3)???????????????????????????????------
>>???????????????????????????????????????2
>>?(%i4)?sum(-k,?k,?-a,?-1);
>>?Is??a??positive,?negative,?or?zero?
>>
>>?n;
>>?????????????????????????????????????????????2
>>??????????????????????????????-?a?+?(-?a?-?1)??-?1
>>?(%o4)????????????????????????--------------------
>>???????????????????????????????????????2
>>?(%i5)?ratsimp(%);
>>??????????????????????????????????????2
>>?????????????????????????????????????a??+?a
>>?(%o5)???????????????????????????????------
>>???????????????????????????????????????2
>>
>>
>>?Should?n't?a?positive?"a"?create?the?same?result?as?%o2?and?a?negative
>>?the?empty?sum,?thus?0??Do?I?miss?something?
>>
>>?Best?Regards
>>
>>?Alexandros
>>?_______________________________________________
>>?Maxima?mailing?list
>>?Maxima at math.utexas.edu
>>?http://www.math.utexas.edu/mailman/listinfo/maxima
>>
>
>First?of?all,?convince?yourself?that
>sum(f(i),i,a,b)?=?-sum(f(i),i,b+1,a-1)?when?a>b,??NOT?zero.
>
>This?is?a?consequence?of
>
>sum(f(i),i,a,b)?+?sum(f(i),i,b+1,c)?=?sum(f(i),i,a,c)
>
>where??a<=b<c
>
>being?extended?to?all?b.
>
>Commercial?Macsyma?has?a?flag?"sumhack"??that?makes?this?true.
>
>A?"negative?sum"?is?not?zero?if?you?maintain?this?identity.
>
>I?think?what?you?are?seeing?is?that?one?part?of?Maxima?believes?this
>identity?and?another?one?doesn't.
>Two?people?can?disagree?on?which?part?of?Maxima?is?in?error.
>
>
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