distance between a point and elements of a matrix

Question

Luis Isaac 2017-4-12

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回答： Luis Isaac 2017-4-21

Dear;

I am looking for an efficient way to compute the distance between coordinates (x,y,z) and the elements of a 3D matrix. For expample for a M3D[1:nx,1:ny,1:nz] I would like to get ahother 3D matrix Distance3D where each element in the new matrix will be:

M3D(ix,iy,iz)=sqrt((ix-x)^2+(iy-y)^2+(iz-z)^2);

Where ix runs for 1 to nx, so on.

Thanks in advance;

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Answer 1

Luis Isaac 2017-4-21

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在 MATLAB Online 中打开

This could be the solution

[ny,nx,nz]=size(M3D);
[xx,yy,zz] = meshgrid((1:nx)-x,(1:ny)-y,(1:nz)-z);
M3D_dist=sqrt(xx.^2 + yy.^2 + zz.^2);

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Answer 2

Fei Deng 2017-4-17

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Are you calculating the distance between coordinates (x,y,z) and the elements of a 3D matrix, OR the distance between coordinates (x,y,z) and the index of a 3D matrix? From your equation, it should be latter case, isn't it? In that case, I probably would just use 3 for-loops.

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Answer 3

Luis Isaac 2017-4-21

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Many Thanks

Yes it is the second; I am traing to calculate de distance from a point with coordinates (x,y,z) and the indexes of a 3D matrix. Of course, 3 for-loops is one of the solution the question, but I am looking for a vectoriced and quicker version of this problem.