from range restriction to domain restriction

*To*: mathgroup at smc.vnet.net*Subject*: [mg72590] from range restriction to domain restriction*From*: "Chris Chiasson" <chris at chiasson.name>*Date*: Thu, 11 Jan 2007 03:16:39 -0500 (EST)

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/