Tensor matrix of speed

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

Answer 1

[Pavan Sahith]

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