Re: How to set y always greater than or equal to x for a function?

*To*: mathgroup at smc.vnet.net*Subject*: [mg46584] Re: [mg46569] How to set y always greater than or equal to x for a function?*From*: Oleksandr Pavlyk <pavlyk at phys.psu.edu>*Date*: Tue, 24 Feb 2004 21:04:34 -0500 (EST)*Organization*: Penn State University; Department of Physics*References*: <200402240333.WAA20733@smc.vnet.net>*Reply-to*: pavlyk at phys.psu.edu*Sender*: owner-wri-mathgroup at wolfram.com

Depending on what you want, you can either proceed by defining you function in the valid domain: Off[Plot3D::plnc]; Off[Plot3D::gval]; Plot3D[If[y - x > 0, Sqrt[y - x]], {x, -100, 100}, { y, -100, 100}, PlotPoints -> 100]; On[Plot3D::plnc]; On[Plot3D::gval]; Then Mathematica complains about function being not a number, and this is why these Plot3D messages are turned off. One alternative way to proceed would be to modify your function, and add Abs under the square root: Plot3D[Sqrt[Abs[y-x]], {x,-100,100},{y,-100,100}] Sasha Albert Franco wrote: > I recently purchased Mathematica 5.0, and I am in the process of > learning how to take advantage of it's many features. > > This is an example of one line I would like to calculate in Mathematica: > > Plot3D[Sqrt[y-x],{x,-100,100},{y,-100,100}]; > > > How can I best edit this line to make y always greater than or equal to x during > calculation so the program doesn't try to take the square root of a > negative number? > > Any help will be appreciated. > > Albert Franco

**References**:**How to set y always greater than or equal to x for a function?***From:*Albert Franco <francoatnsuok@earthlink.net>