1
$\begingroup$

This question already has an answer here:

How to get the output graph which consider only x^2+y^2=4 (the boundary of the region only)? I found this on the Help.

Plot3D[{x^2 + y^2, -x^2 - y^2}, {x, -2, 2}, {y, -2, 2}, 
RegionFunction -> Function[{x, y, z}, x^2 + y^2 <= 4], 
BoxRatios -> Automatic]

When I change <= to ==, no output comes. Or do I need to use different command?

$\endgroup$

marked as duplicate by Szabolcs, m_goldberg plotting Nov 21 '16 at 11:51

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

2
$\begingroup$

There needs to be a finite thickness

Plot3D[{x^2 + y^2, -x^2 - y^2},
 {x, -2, 2}, {y, -2, 2},
 RegionFunction ->
  Function[{x, y, z}, 3.9 <= x^2 + y^2 <= 4],
 PlotPoints -> 75,
 MaxRecursion -> 6,
 BoxRatios -> Automatic]

enter image description here

$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.