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Re: different output!!

  • To: mathgroup at smc.vnet.net
  • Subject: [mg97022] Re: different output!!
  • From: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>
  • Date: Mon, 2 Mar 2009 05:22:58 -0500 (EST)
  • References: <godm3n$46c$1@smc.vnet.net>

It seems correct to me. Please note that Mod[x,5] is not necessarily
integer and therefore not countable if x is a real whereas it is
countable when x is an integer. Reduce does a fine job here.

Cheers -- Sjoerd


On Mar 1, 11:56 am, olfa <olfa.mra... at yahoo.fr> wrote:
> Hi Mathematica community,
> Why output2 (with integers as domain) is different from output1 (with
> reals as domain) ?!! I think it should be the same thing.
>
> input1:Reduce[{Mod[x, 5] == Mod[xP, 5], 0 <= xP < 5}, {xP}, Reals,
>  Backsubstitution -> True]
>
> output1: 0 <= Mod[x, 5] < 5 && xP == Mod[x, 5]
>
> input2:Reduce[{Mod[x, 5] == Mod[xP, 5], 0 <= xP < 5}, {xP}, Integer=
s,
>  Backsubstitution -> True]
>
> output2: (Mod[x, 5] == 0 && xP == 0) || (Mod[x, 5] == 1 &&
>    xP == 1) || (Mod[x, 5] == 2 && xP == 2) || (Mod[x, 5] =
== 3 &&
>    xP == 3) || (Mod[x, 5] == 4 && xP ==
> 4)



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