How to assume that a function is positive?

*To*: mathgroup at smc.vnet.net*Subject*: [mg114294] How to assume that a function is positive?*From*: Sam Takoy <sam.takoy at yahoo.com>*Date*: Tue, 30 Nov 2010 04:04:07 -0500 (EST)

Hi, Who do I let Mathematica know that a function f is positive for all arguments? For example, how do I make the following work (I think my intention is clear): Assuming[f[x] > 0, (f[x + y]^2)^(1/2) // Simplify] Many thanks in advance, Sam