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

*To*: mathgroup at smc.vnet.net*Subject*: [mg46577] RE: [mg46569] How to set y always greater than or equal to x for a function?*From*: David.Annetts at csiro.au*Date*: Tue, 24 Feb 2004 21:04:24 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Hi Albert, > 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? What's wrong with Plot3D[If[y >= x, Sqrt[y - x]], {x, -100, 100}, {y, -100, 100}]; If the warning messages bother you, investigate If[...] further, and adjust the PlotRange accordingly. Regards, Dave.