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MathGroup Archive 2004

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Re: seruous solve bug? only when used with simplifying

  • To: mathgroup at smc.vnet.net
  • Subject: [mg48690] Re: seruous solve bug? only when used with simplifying
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 10 Jun 2004 02:44:23 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <ca6haa$fef$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

ohhh the situation is even mutch wronger than you think,
you don't need to use Simplify[] and FullSimplify[] to
find the bug just try


and get False, the situation is just the same
with

TrueQ[a^2+2*a*b+b^2==(a+b)^2]

and if you would like to read the manual what TrueQ[]
does and what Equal[] mean than it would be clear that
you have not found a bug. 

And yes Simplify[] and FullSimplify[] change the
system so much that they are not Equal[] but the
system is still equal, because the Mathematica function
Equal[] has a different meaning than "equal".

Then only solution to the problem above is to use

TrueQ[2*a + 2*b == 2(a + b) // FullSimplify]
TrueQ[a^2 + 2*a*b + b^2 == (a + b)^2 // FullSimplify]

but you can't use it, because you just found out that
it has "serious ... bug" too bad.

Regards
  Jens


sean kim wrote:
> 
> hello group,
> 
> i think i have a serious Solve[], Simplify[], FullSimplify[] bug...
> 
> Take a system of equations as below. (apb is actually (a+b). i defined
> it as apb to keep Mathematica crunching away at it)
> 
> sys =
> {c1[t] == (c*(16*a^4 + 8*a^3*kd + 4*a^2*apb*kd + 2*a*apb^2*kd +
> apb^3*kd))/(apb^4*kd),
> c2[t] == (2*(8*a^3 + 4*a^2*apb + 2*a*apb^2 + apb^3)*b*c)/(apb^4*d),
> c3[t] == (2*(8*a^3 + 4*a^2*apb + 2*a*apb^2 + apb^3)*b*c)/(apb^4*kd)}
> 
> sys1 = sys /.{apb -> (a + b)}
> sys2 = sys/.{apb -> (a + b)}//Simplify
> sys3 = sys/.{apb -> (a + b)}//FullSimplify
> 
> and then use
> 
> TrueQ[sys1 == sys1]
> TrueQ[sys1 == sys2]
> TrueQ[sys1 == sys3]
> TrueQ[sys2 == sys3]
> 
> then it gives,
> 
> Out[18]=True
> Out[19]=False
> Out[20]=False
> Out[21]=False
> 
> Simplify and FullSimplify changed the system so much that they are not
> equal?
> 
> Basically, unless I define the (a+b) as a single constant apb, the Mathematica
> will do soemthing with it then it messes it up. I think...
> 
> Why is this happening? and how do i prevent it from happening again
> with other more obsucre systems?  Above I got lucky in finding the
> cause (a+b)
> 
> thanks in advance for any and all comments.
> 
> Sean


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