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Conditionals ("If") and definitions for 3D plots

  • To: mathgroup at
  • Subject: [mg14094] Conditionals ("If") and definitions for 3D plots
  • From: "Julio Vera" <lvera at>
  • Date: Fri, 25 Sep 1998 03:15:20 -0400
  • Sender: owner-wri-mathgroup at

Hello. This is my first posting to the list. I'm very new to
Mathematica.  I have studied quite a bit of The Mathematica Book in the last 2 weeks,

A few questions.
1) How to give NO value to the "else" parameter of the function
If[expr, then, else]

I want a function to be defined ONLY if the condition is true. I tried
to leave a blank, a space, and to put the "not exist" symbol, with no

I tried the "Which" function too.

2) How to define a dominium range (for a function to be plotted) by
means of an equation

Instead of giving a maximum and a minimum value to the variables
involved (by expressions like  {x,-1,1},{y,-1,1}), use a function, maybe
an implicit one like 4x^2+y^2==1 . 

3) ImplicitPlot3D

For Plot, we have Plot3D. Same thing with ParametricPlot and
ParametricPlot3D. But I cannot find an equivalent tridimensional
function to ImplicitPlot. I have used the normal Mathematica functions, and
those in the Graphics' package.

Thanks for your help and your time. 

Julio Vera

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