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MathGroup Archive 2004

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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.


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