General--IF condition in Plot3D

• To: mathgroup at smc.vnet.net
• Subject: [mg68972] General--IF condition in Plot3D
• Date: Sat, 26 Aug 2006 02:03:54 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```Hi All,

How to use a IF condition in Plot3D??

For example:
I have "I" values caluclated by I=P/2*Pi*r*L .; where P=10.3,L=0.45,r=dist.
So if i want to plot "I" when "r<x", how to do it??
(Here i am giving my procedure thru which i am getting a Plot with some warning)
r[x_,y_]:=Sqrt[x^2+y^2];
I[x_,y_]:=P/2*Pi*r[x_,y_]*L
Plot3D[If[r[x,y]<=0.082,I[x,y]],{x,-0.082,0.082},{y,-0.082,0.082}]

Then i am getting following warnings:
1. Plot3D::"plnc" :
If[(r[x, y]<=0.82),I[x, y] is neither a machine-size real number at {x,y}=(-0.058,-0.082) nor a list of a real number and a valid color directive.

2. General::"stop": Further output of Plot3D :: plnc will be suppressed during this calculation.

3. Plot3D::"gval": Function value (Null) at grid point xi = 1, yi = 1 is not a real number.

4. General::"stop": "Further output of Plot3D :: gval will be suppressed during this calculation."

Is there anything wrong in the syntax or range specification.
I am clueless. Please provide me ur valueable suggestions.