Vectorising a Meshgrid Coordinate Construction

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ADSW121365 2020-9-2

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https://ww2.mathworks.cn/matlabcentral/answers/588052-vectorising-a-meshgrid-coordinate-construction

评论： ADSW121365 2020-9-3

采纳的回答： Bruno Luong

Gauss_Points.mat

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I have three coordinate arrays (file attached) of size [M x 2], where M is the number of elements and the 2 represents different points in a 1D system. To find the 3D meshed coordinates upon which I perform calculations I use code of the form:

for ele = 1:size(X_co,1) %Loop Over Each Element
    [X_cube,Y_cube,Z_cube] = meshgrid(X_co(ele,:),Y_co(ele,:),Z_co(ele,:)); %Construct Meshgrid of size [2x2x2] for an Element
    X_save(:,:,:,element) = X_cube; %Save Coordinates
    Y_save(:,:,:,element) = Y_cube;
    Z_save(:,:,:,element) = Z_cube;    
end

The solution then is of size [2x2x2xM]. My best attempt to vectorise this was:

[X_cube,Y_cube,Z_cube] = meshgrid(X_co,Y_co,Z_co);  
X_save = reshape(X_cube,2,2,2,[]); Y_save = reshape(Y_cube,2,2,2,[]);  Z_save = reshape(Z_cube,2,2,2,[]); 

However this solution is of size [2x2x2x(M^3)] which, when plotting both solutions has many many many repeated points so doesn't actually work for my application.

Can this problem be vectorised, or is a for loop the best way to construct this coordinate array?

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jessupj 2020-9-2

ndgrid is the way to go here i think. i think it can be done using meshgrid along with some resize + repmat statements.

ADSW121365 2020-9-2

编辑：ADSW121365 2020-9-2

在 MATLAB Online 中打开

https://uk.mathworks.com/matlabcentral/answers/588052-vectorising-a-meshgrid-coordinate-construction#comment_994471

This maybe niave implementation, but:

[XO,YO,ZO] = ndgrid(X_co,Y_co,Z_co)

seems to give the same solution as:

[X_cube,Y_cube,Z_cube] = meshgrid(X_co,Y_co,Z_co);  
X_save = reshape(X_cube,2,2,2,[]); Y_save = reshape(Y_cube,2,2,2,[]);  Z_save = reshape(Z_cube,2,2,2,[]); 

which isn't what I'm looking for. Could you guys elaborate a little more please? (Some example arrays are attached to the main post)

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采纳的回答

Bruno Luong 2020-9-2

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/588052-vectorising-a-meshgrid-coordinate-construction#answer_488764

编辑：Bruno Luong 2020-9-2

在 MATLAB Online 中打开

One way

[~,nx] = size(X_co);
[~,ny] = size(Y_co);
[m,nz] = size(Z_co);
[NX,NY,NZ] = meshgrid(1:nx,1:ny,1:nz);
sz = [size(NX),m];
% if you know nx, ny, nz are 2 you can replace the 5 above commands by
% [NX,NY,NZ] = meshgrid(1:2);
% sz = [2,2,2,m];
X_save = X_co.';
Y_save = Y_co.';
Z_save = Z_co.';
X_save = reshape(X_save(NX,:),sz);
Y_save = reshape(Y_save(NY,:),sz);
Z_save = reshape(Z_save(NZ,:),sz);