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Re: FindInstance does not abort with TimeConstrained

  • To: mathgroup at smc.vnet.net
  • Subject: [mg115511] Re: FindInstance does not abort with TimeConstrained
  • From: Albert Retey <awnl at gmx-topmail.de>
  • Date: Thu, 13 Jan 2011 03:26:24 -0500 (EST)
  • References: <igis66$pl0$1@smc.vnet.net> <igjr3t$95j$1@smc.vnet.net>

Hi,

> Thanks for everyone's replies. Indeed, the equations which I provided
> have no root. I included the Chop + FullSimplify because that is when
> FindInstance hangs and can only be aborted by killing the kernel.
> After further investigation, I realize that this happens in version 8
> but not in version 7, which returns the correct output (no solution)
> instantly. Hence, I have reverted back to version 7 for the moment.
> 
> Nevertheless, could there possibly be a bug in version 8's
> FindInstance? Thanks.

I'm really no expert in that field, but from the documentation and name
of FindInstance I would not expect that if it returns an empty list that
means there are no instances, it merely means that it gave up in trying
to find one. So I wouldn't in that case consider version 7's behaviour
to be better than that of 8: both mean that it couldn't find an instance
(in finite time). That can of course be because there is none, it could
also mean that the algorithms in FindInstance just can't find them. If
you want to "proof" that there are no solutions I don't think that
FindInstance can do more for you than possibly find contradicting
examples...

hth,

albert




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