# Tensor matrix of speed

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JORGE ORDOÑEZ CARRASCO am 15 Feb. 2022
Beantwortet: Pavan Sahith am 10 Nov. 2023
Hi everyone i got confused in tensor matrix of matlab, i have a code which calculates position and speed of 1000 particle update the position and speed, so i have a double for running one for the particles and the other for the next step, particle position and speed is updated and i need to save some positions and speed to see the this evolution. But im confuse i have this code:
As you can see bellow the matrix obtained (A(n_particle x 3 x n_steps)) the front of the cube, as i get it is read A(:,:,1) , but i need to obtain the top of this cube in the logic of matlab i know is A(1,:,:) but it only returns the first row data. I expect a tensor dimensions n_particle x 3 x n_steps for particle 1 i expect to see the evolution, what im doing wrong?
Thank you
for i=1:n_particles
for j=1:n_steps
Here i do my calculations
x_position=newposition
u_speed=newespeed
A(i,:,j)=newposition %supposely a particle i has j steps
B(i,:,j)=newspeed
end
end
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### Antworten (1)

Pavan Sahith am 10 Nov. 2023
Hello,
I understand you have matrix 'A' with dimensions (n_particle x 3 x n_steps) and you want to see the evolution of particle 1 so the output would be of dimensions (1 x 3 x n_steps).
When I tried with a random matrix, I can obtain the top of the matrix as a tensor.
I assume a matrix K with dimensions (2,1,3) , as you know, if you want to obtain the face of the matrix you can use K(:,:,1)
K=rand(2,3,2)
K =
K(:,:,1) = 0.7054 0.0411 0.2007 0.9059 0.6021 0.9900 K(:,:,2) = 0.3477 0.3194 0.3143 0.9252 0.1851 0.2113
K(:,:,1);
To obtain the top of the matrix as a tensor, you can use K(1,:,:)
K(1,:,:)
ans =
ans(:,:,1) = 0.7054 0.0411 0.2007 ans(:,:,2) = 0.3477 0.3194 0.3143
To make the analysis of evolution easier , you can try using the "squeeze" function to store all rows at the top of 'K' in a 2D matrix. This function returns an array with the same elements as the input array 'K', but with dimensions of length 1 removed.
m=squeeze(K(1,:,:))'
m = 2×3
0.7054 0.0411 0.2007 0.3477 0.3194 0.3143
Please refer to the MathWorks documentation to know more about
1. "Multidimensional Arrays"-https://in.mathworks.com/help/matlab/math/multidimensional-arrays.html
2. "squeeze"-https://in.mathworks.com/help/matlab/ref/squeeze.html
Hope that helps
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