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Re: Reduce in Mathematica 5 vs Mathematica 8 (2nd problem)

  • To: mathgroup at smc.vnet.net
  • Subject: [mg115357] Re: Reduce in Mathematica 5 vs Mathematica 8 (2nd problem)
  • From: Albert Retey <awnl at gmx-topmail.de>
  • Date: Sat, 8 Jan 2011 03:41:26 -0500 (EST)
  • References: <ig0bsm$sbl$1@smc.vnet.net>

Am 05.01.2011 00:52, schrieb olfa:
> Hi Mathematica Community,
> 
> First,wish you happy and successfull new year.
> 
> For this 2nd problem in the same subject,I have this system to solve:
> 
> Reduce[Not[
>   ForAll[{aaP, abP, iP, jP, sP, tP, uP, xP, yP, zP},
>    Implies[t == tP && i + x == iP + xP && y == yP &&
>      j t + z == jP tP + zP && t x + z == tP xP + zP &&
>      Floor[Log[j]/Log[2]] == Floor[Log[jP]/Log[2]] &&
>      Floor[Log[x]/Log[2]] == Floor[Log[xP]/Log[2]] && x >= xP,
>     t x == tP xP]]]]
> 
> in mathematica 5 the output is given in a very short time and is "the
> system cannot be solved with the method available to Reduce" this
> suits me (although I wish it to be  the output "True" which is the
> right answer)
> 
> in mathematica 8 the kernel still in running indefinitely and this
> does not suit me at all :(
> 
> so how to deal with that?

Assuming that you do not now a priory whether Reduce will succeed in a
given time or not, then zou will have to decide on how long you want to
wait for an answer. This will give up after 10 seconds:

TimeConstrained[
 Reduce[Not[
   ForAll[{aaP, abP, iP, jP, sP, tP, uP, xP, yP, zP},
    Implies[t == tP && i + x == iP + xP && y == yP &&
      j t + z == jP tP + zP && t x + z == tP xP + zP &&
      Floor[Log[j]/Log[2]] == Floor[Log[jP]/Log[2]] &&
      Floor[Log[x]/Log[2]] == Floor[Log[xP]/Log[2]] && x >= xP,
     t x == tP xP]]]],
 10, $Failed
 ]

hth,

albert


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