       Re: About Reduce and Mod

• To: mathgroup at smc.vnet.net
• Subject: [mg96926] Re: About Reduce and Mod
• From: dh <dh at metrohm.com>
• Date: Fri, 27 Feb 2009 06:14:33 -0500 (EST)
• References: <go63mv\$psm\$1@smc.vnet.net>

```
Hi,

Mathematica calculates by default with complex number. You must tell it that you

are looking for real numbers by e.g. specifying a domain:

Reduce[{Mod[x, 5] == Mod[xP, 5], 0 <= xP < 5}, {xP}, Reals,

Backsubstitution -> True]

hope this helps, Daniel

olfa wrote:

> Hi Mathematica community,

> I have this input:   Reduce[{Mod[x, 5] == Mod[xP, 5], 0 <= xP < 5},

> {xP}, Backsubstitution -> True]

> Mathematicas gives me this output:0 <= Re[Mod[x, 5]] < 5 && Im[Mod[x,

> 5]] == 0 && xP == Mod[x, 5]

> 1)but why there is 0 <= Re[Mod[x, 5]] < 5 && Im[Mod[x, 5]] == 0 as

> part of the output ?

> 2) and how could I eliminate it (by adding something in reduce for

> example) because all that I want is only this output xP == Mod[x, 5]?

>

> thank you very much.

>

```

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