Re: About Reduce and Mod

*To*: mathgroup at smc.vnet.net*Subject*: [mg96942] Re: About Reduce and Mod*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Fri, 27 Feb 2009 06:17:36 -0500 (EST)

On 2/26/09 at 7:59 AM, olfa.mraihi at yahoo.fr (olfa) wrote: >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 ? Mathematica by default assumes all variables can take on complex values. The output is specifying the conditions on a complex variable needed to make the equality hold. >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]? In[4]:= Assuming[Element[{x, xP}, Reals], Refine[ Reduce[{Mod[x, 5] == Mod[xP, 5], Mod[xP, 5], 0 <= xP < 5}, {xP}, Backsubstitution -> True]]] Out[4]= xP == x mod 5