Re: from range restriction to domain restriction

*To*: mathgroup at smc.vnet.net*Subject*: [mg72606] Re: [mg72590] from range restriction to domain restriction*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Fri, 12 Jan 2007 05:09:35 -0500 (EST)*Reply-to*: hanlonr at cox.net

Reduce[Sqrt[x]>=0||Sqrt[x]<0,x] x >= 0 Plot[Evaluate[Piecewise[{{Sqrt[x], Reduce[Sqrt[x]>=0||Sqrt[x]<0,x]}}]], {x,-5,5},PlotStyle->Red]; Bob Hanlon ---- Chris Chiasson <chris at chiasson.name> wrote: > If I wanted to ensure that Sqrt[x] was always a real number, perhaps > as a condition on Piecewise, I would say Im@Sqrt@x==0 (or > Element[Sqrt@x,Reals], but Mathematica doesn't like to simplify that). > In my real case, x isn't a symbol - and it comes from the output of > some other commands. However, I also know that Element[x,Reals], so I > was wondering if there is a way to make Mathematica do the following: > > (part of) input: > Im@Sqrt@x==0 > > output: > x>0 > > If someone knows how to do this (other than the obvious Cases + > pattern transformation), I would appreciate being told how. Thank you. > > -- > http://chris.chiasson.name/ >