Reshape 2D matrix to 3D using time as 3rd dimension

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iijoclu
iijoclu 2015-10-28
编辑： Matt J 2021-3-12
Hi,
I've got a A = n x n matrix and I want to convert this 2D matrix to a 3D one using time as the third dimension. So the 3D should show how the value of all the elements in the n x n matrix changes with respect to time.
I tried using the reshape function but to no avail.
Thanks!

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Thorsten
Thorsten 2015-10-28
If i is your related to your time and takes values 1,2,3, etc, and A is the n x n matrix at time point i, you can use:
B(:,:,i) = A;
  2 个评论
iijoclu
iijoclu 2015-10-28
编辑：iijoclu 2015-10-28
Ok so my time function is basically
[kgrid.t_array, dt] = makeTime(kgrid, medium.sound_speed);
When I try to plug kgrid.t_array in the formula above, I get an error saying that the subscripts should be real positive integers or logical.
Size of my kgrid.t_array is [1 5243].
Thorsten
Thorsten 2015-10-28
编辑：Thorsten 2015-10-28
You cannot use the values of kgrid.t_array, but instead 1:numel(kgrid.t_array). Your code should look something like below, assuming that you have a function that computes your NxN matrix for every timestep:
for i=1:numel(kgrid.t_array)
t = kgrid.t_array(i); % get the ith time value
A = computeNxNmatrix(t, more parameters); %
B(:,:,i) = A;
end

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更多回答（1 个）

Matt J
Matt J 2015-10-28
I tried using the reshape function but to no avail.
Be more persistent. RESHAPE is the appropriate thing to use.
  2 个评论
lmaree
lmaree 2021-3-12
"Beyond the second dimension, the output, B, does not reflect trailing dimensions with a size of 1. For example, reshape(A,3,2,1,1) produces a 3-by-2 matrix." from the reshape documentation.
In my case, this is exactly what I need to multiply a spacial 2D matrix with a time vector. However, reshape doesn't have the functionality it seems...
Matt J
Matt J 2021-3-12
编辑：Matt J 2021-3-12
Ran in:
It is not needed. There is no difference between what you can do with a 3x2 matrix and with a 3x2x1x1 matrix.
A=rand(3,2);
t=rand(1,1,1,4);
A.*t
ans =
ans(:,:,1,1) = 0.2134 0.1069 0.0927 0.5706 0.2873 0.2506 ans(:,:,1,2) = 0.1807 0.0905 0.0785 0.4833 0.2433 0.2123 ans(:,:,1,3) = 0.3407 0.1707 0.1481 0.9111 0.4586 0.4002 ans(:,:,1,4) = 0.0462 0.0232 0.0201 0.1236 0.0622 0.0543

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