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MathGroup Archive 2005

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Re: Bug in Reduce?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg60470] Re: Bug in Reduce?
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Sat, 17 Sep 2005 02:31:51 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, U.K.
  • References: <dgdulf$1ad$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Bob Hanlon wrote:
> $Version
> 
> 5.2 for Mac OS X (June 20, 2005)
> 
> Reduce[{a c-b d==0,a d+b c==0},
>     {a,b,c,d},Reals]//Simplify
> 
> (a == 0 && b == 0) || (c == 0 && d == 0)
> 
> 
> Bob Hanlon
> 
> 
>>From: "Kennedy" <jack at realmode.com>
To: mathgroup at smc.vnet.net
>>Date: 2005/09/15 Thu AM 05:16:26 EDT
>>Subject: [mg60470]  Bug in Reduce?
>>
>>The source of this apparent bug could be my misunderstanding of the 
> 
> middle, 
> 
>>"vars" parameter of Reduce, but it sure seems like the following output 
>>indicates that  c  must be  0  for my two equations to be satisfied, when in 
>>fact if  a  and  b  are both  0,  c  does not need to be  0.
>>
>>Regards,
>>Jack
>>
>>In[1]:=
>>Reduce[{a c - b d == 0, a d + b c == 0}, {a, b, c, d}, Reals] // 
>>FullSimplify
>>
>>Out[1]=
>>c == 0 && (d == 0 || (a == 0 && b == 0))
>>
>>(version 5.1 for Windows) 
>>
>>
> 
> 
In[1]:=
FullSimplify[Reduce[{a*c - b*d == 0, a*d + b*c == 0},
    {a, b, c, d}, Reals]]

Out[1]=
(a == 0 && b == 0) || (c == 0 && d == 0)

In[2]:=
$Version

Out[2]=
"5.2 for Microsoft Windows (June 20, 2005)"

Regards,
/J.M.


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