Re: solve and Abs

*To*: mathgroup at smc.vnet.net*Subject*: [mg69397] Re: solve and Abs*From*: Peter Pein <petsie at dordos.net>*Date*: Sun, 10 Sep 2006 07:20:34 -0400 (EDT)*References*: <edtrmv$le6$1@smc.vnet.net>

Richard J. Fateman schrieb: > Is there a reason (in 5.1) for Solve[x-Abs[x]==0,x] to return {{}}? > This supposedly means all variables can have all possible values. > > Reduce does better. > Hello, the result {{}} means that Solve did not find values for x, which fulfill the equation without "special conditions". The help browser tells us: "Solve gives generic solutions only. It discards solutions that are valid only when the parameters satisfy special conditions. Reduce gives the complete set of solutions. " The special condition in this case is obviously x>=0. Greetings, Peter

**Follow-Ups**:**Re: Re: solve and Abs***From:*Murray Eisenberg <murray@math.umass.edu>