integrate returns undefined .. Bug in zero denominator?

If you are not going to allow anything other than 100% correct answers, that 
would make answers much more complicated wouldn't it?  In engineering you 
have to compromise between an ideal answer verses a 100% correct one.  I 
suppose that has already been done in Maxima, so I take it back.

Rich




----- Original Message ----- 
From: "Richard Fateman" <fateman at cs.berkeley.edu>
To: "'Richard Hennessy'" <rvh2007 at comcast.net>
Cc: <maxima at math.utexas.edu>
Sent: Wednesday, September 10, 2008 11:38 AM
Subject: RE: [Maxima] integrate returns undefined .. Bug in zero 
denominator?


> The result from solve is clearly not a solution.  But your proposed 
> solution
> is not right because
> x= y+n*%pi,  n integer and nonzero IS a solution.
>
> The point I was trying to make is that you cannot say it is ok to be
> just a little slipshod because you yourself
> will be aware of something  (like a denominator being zero).
>
> There are enough subtle problems with detecting zero that you can't always
> do it.
> But that's not a positive feature.
>
> Once you are aware of a "feature" that is really a bug, you can construct
> many erroneous
> results, as Vladimir Bondarenko does, on sci.math.symbolic.
>
> RJF
>
>
>> -----Original Message-----
>> From: Richard Hennessy [mailto:rvh2007 at comcast.net]
>> Sent: Wednesday, September 10, 2008 8:23 AM
>> To: fateman at EECS.Berkeley.EDU
>> Cc: maxima at math.utexas.edu
>> Subject: Re: [Maxima] integrate returns undefined
>>
>> Rich,
>>
>> Automatic taking of limits is not always the answer for many people.
>> Personnally I would like this feature
>> (%i1) solve (sin(x-y)/(x-y)=0,x);
>> (%o1) []
>>
>> since I think a "solution" that makes the demominator zero is
>> never "right".
>>
>> Rich
>>
>>
>> ----- Original Message ----- 
>> From: "Richard Fateman" <fateman at cs.berkeley.edu>
>> To: "'Richard Hennessy'" <rvh2007 at comcast.net>
>> Cc: <maxima at math.utexas.edu>
>> Sent: Wednesday, September 10, 2008 11:04 AM
>> Subject: RE: [Maxima] integrate returns undefined
>>
>>
>> > Your saying that something is not a bug does not mean
>> everyone will agree
>> > with you.
>> > Or even that it will result in non-buggy results.  Many
>> "bugs" reported on
>> > sci.math.symbolic
>> > by one writer as bugs in "integrate"  in Maple, are bugs in
>> > simplification,
>> > sometimes
>> > just like this "obvious" but sometimes wrong feature.
>> >
>> > In particular, you may not need reminding about a=0 in this
>> case, but what
>> > about
>> > in other cases, where Maxima just goes ahead without you... e.g.
>> > solve (sin(x-y)/(x-y)=0,x)
>> >
>> > returns x=y;
>> > but this is not a solution, which can be seen either by direct
>> > substitution
>> > or
>> > taking a limit.
>> >
>> > RJF
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >> -----Original Message-----
>> >> From: Richard Hennessy [mailto:rvh2007 at comcast.net]
>> >> Sent: Wednesday, September 10, 2008 7:26 AM
>> >> To: fateman at EECS.Berkeley.EDU; 'John Pye'; maxima at math.utexas.edu
>> >> Cc: 'Edwin Woollett'
>> >> Subject: Re: [Maxima] integrate returns undefined
>> >>
>> >> This is not a bug, this simplifies to 1
>> >>
>> >> a/a -> 1
>> >>
>> >> with no assumptions made.  I have noticed that in general
>> >> radcan(expr1/expr1) simplifies to 1 and Maxima never says
>> >> except when expr1
>> >> = 0.  Which I find useful since I know about the possibility
>> >> that expr1
>> >> could be zero but I don't really need to be reminded of
>> this case.  I
>> >> definitely would not want to be asked is expr1 = zero all the
>> >> sime when
>> >> cancelling terms.  That would be annoying.
>> >>
>> >> Rich
>> >>
>> >>
>> >> ----- Original Message ----- 
>> >> From: "Richard Fateman" <fateman at cs.berkeley.edu>
>> >> To: "'John Pye'" <john.pye at anu.edu.au>; <maxima at math.utexas.edu>
>> >> Cc: "'Edwin Woollett'" <woollett at charter.net>
>> >> Sent: Tuesday, September 09, 2008 11:56 PM
>> >> Subject: Re: [Maxima] integrate returns undefined
>> >>
>> >>
>> >> > Not so clear a bug.
>> >> > (n-m)/(n-m) simplifies to 1.
>> >> > But if you know n=m, then you have 0/0.  So is it a bug if
>> >> (n-m)/(n-m) -->
>> >> > 1?
>> >> >
>> >> > Answer: maybe. But not clear :)
>> >> >
>> >> > RJF
>> >> >
>> >> >
>> >> >> -----Original Message-----
>> >> >> From: maxima-bounces at math.utexas.edu
>> >> >> [mailto:maxima-bounces at math.utexas.edu] On Behalf Of John Pye
>> >> >> Sent: Tuesday, September 09, 2008 6:47 PM
>> >> >> To: maxima at math.utexas.edu
>> >> >> Cc: Edwin Woollett
>> >> >> Subject: Re: [Maxima] integrate returns undefined
>> >> >>
>> >> >> I can confirm that behaviour; it looks like a clear bug to me.
>> >> >>
>> >> >> Cheers
>> >> >> JP
>> >> >>
>> >> >> Edwin Woollett wrote:
>> >> >> > integrate(..) returns undefined when it
>> >> >> > should know the answer.
>> >> >> >
>> >> >> > (%i1) declare( [ m, n ], integer )$
>> >> >> > (%i2) assume ( m > 0,  n > 0 )$
>> >> >> > (%i3) integrate( cos(m*x)^2, x, 0, 2*%pi );
>> >> >> > (%o3)                                 %pi
>> >> >> > (%i4) integrate( cos(m*x)*cos(n*x), x, 0, 2*%pi  );
>> >> >> > Is  n - m  positive, negative, or zero?
>> >> >> >
>> >> >> > zero;
>> >> >> > (%o4)                              undefined
>> >> >> >
>> >> >> > Is this a known bug?
>> >> >>
>> >> >> _______________________________________________
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>> >> >> Maxima at math.utexas.edu
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>> >> >>
>> >> >
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>> >>
>> >>
>> >
>>
>>
>