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

• To: mathgroup at smc.vnet.net
• Subject: [mg115260] Re: Reduce in Mathematica 5 vs Mathematica 8 (2nd problem)
• From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
• Date: Wed, 5 Jan 2011 05:48:33 -0500 (EST)

```On 5 Jan 2011, at 00:53, olfa wrote:

> 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] == Floor[Log[jP]/Log] &&
>     Floor[Log[x]/Log] == Floor[Log[xP]/Log] && 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
>
> in mathematica 8 the kernel still in running indefinitely and this
> does not suit me at all :(
>
> so how to deal with that?
>
>

e.g

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] == Floor[Log[jP]/Log] &&
Floor[Log[x]/Log] == Floor[Log[xP]/Log] && x >== xP,
t x == tP xP]]]], 5]

\$Aborted

Andrzej Kozlowski

P.S. You should have noticed by now that Reduce can never deal with anything involving Floor. See, for example:

In:== Reduce[Floor[x] <== x && x > 0, x, Reals]

During evaluation of In:== Reduce::nsmet:This system cannot be solved with the methods available to Reduce. >>

Out== Reduce[Floor[x] <== x && x > 0, x, Reals]

```

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