Removing the origin from the 3D meshgrid?

Question

Omar Azami 2020-2-19

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/506431-removing-the-origin-from-the-3d-meshgrid

回答： darova 2020-2-19

Suppose I want to plot level surfaces of a function of 3 variables, and suppose this function has a 1/(r^n) dependence. Where r = sqrt(X.^2 + Y.^2 + Z.^2) is the distance from the origin. Naturally I want to filter the origin from the [X,Y,Z] meshgrid to avoid singularities. How do I do this? Here is my attempt.

I thought about using the nonzero function on vectors x,y, and z and then forming the meshgrid but then that excludes entire coordinate planes.

%1) Create the grid
n = 50;
rmax = 2400;
x = linspace(-rmax,rmax,n+1);
y = linspace(-rmax,rmax,n+1);
z = linspace(-rmax,rmax,n+1);
[X,Y,Z] = meshgrid(x,y,z);
%2) Create R
R = sqrt(X.^2 + Y.^2 + Z.^2);
R1 = R.^(-1);    %Create the reciprocal of R
idx = isnan(R1); %Find all the NaNs
R(idx) = [];     %Delete all the NaN's in R, do the same for X,Y,Z
X(idx) = [];
Y(idx) = [];
Z(idx) = [];

Despite there being obvious singularities in R1 (because x,y,z each contain zero) I am still getting R,X,Y,and Z to have the same number of elements as they did before.

I would greatly appreciate any help.