How to convert a matrix into a 3d matrix

Hi i have a function that is creating a matrix. How do i create a vector that takes this matrix and adds n dimensions to it, i.e makes it 3d???

[sixwwwwww]

do you just want to replicate it N times?

[Jos (10584)]

What do you exactly mean by "a vector that takes this matrix and adds n dimensions"?

Tip: if English is a problem when you're not a native speaker (like me), a question is often clarified by adding a short example.

[Image Analyst]

Do you mean "a function" instead of "a vector"???

Answer 1

[sixwwwwww]

here is an example to repeat a matrix N times in the 3rd dimension

a = rand(10); % your matrix
b = repmat(a, 1, 1, 5); % makes multiple copies of your matrix in 3rd dimension

I hope it helps. Good luck!

Answer 2

[Giovanni]

Thanks guys. What i currently have is a function which produces n lots of a vector Time, but its values are different each time. I want to combine all this vectors into one 3d matrix, does this help? Thanks in advance

[sixwwwwww]

how do you want to combine them in 3D how they should be combined?

[Giovanni]

thanks for your help man. When i ran my loop i will produce say 5 matrix. Then i want to put all this together in a 3d vector

Answer 3

[Image Analyst]

If you're in a loop, you can do

for k = 1 : numberOfLoopIterations
  thisMatrix = yourFunction();
  if k == 1
     % Start it/initialize it.
     matrix3D = thisMatrix;
  else
     % Append this matrix in 3D to the "master" one.
     matrix3D = cat(3, matrix3D, thisMatrix); 
  end
end

[Giovanni]

but what is matrix 3D, in your code you assigned matrix 3d in both sides

[Image Analyst]

matrix3D is the 3D matrix you're building up, iteration by iteration by appending new 2D matrices to it. I am not assigning it on both sides. I'm using it on the right to make a new one on the left.

[Giovanni]

im quite new to matlab so sorry if this seems dumb but when i run this code i keep getting unassigned variable matrix 3D

[Giovanni]

oh i get it now. However now i have a new problem. Can you concatenate vectors with different dimension into one 3d vector?

[Image Analyst]

No, the array must be rectangular. You can't have any "ragged" edges. If you need that, then you need to use cell arrays, which is a lot more complicated). See http://matlab.wikia.com/wiki/FAQ#What_is_a_cell_array.3F

Answer 4

[Walter Roberson]

As you asked the question again, I will repeat what Image Analyst said, but with different wording:

In order to combine vectors unchanged into a numeric matrix, the vectors must all be the same length. There is no way to overcome this limitation in a numeric matrix.

You can chop all the vectors down to the same length, by throwing away information. After that you can use cat() to combine them into a numeric matrix.

You can extend the short vectors with some value (such as 0 or inf or NaN) so that the vectors are all the same length. After that you can use cat() to combine them into a numeric matrix.

Now another option: if you have several vectors of coordinates (such as time) and corresponding values, then you can determine some "representative" coordinates and use interp1() to interpolate the values at the representative coordinates, for each vector. After that you can use cat() to combine the interpolated values into a numeric matrix. For example:

L1 = length(v1); L2 = length(v2); L3 = length(v3);
new_L = mean([L1, L2, L3]);    %number of points we will interpolate at
all_v = vertcat(v1(:), v2(:), v3(:));   %combine all of the vectors
minv = min(all_v);
maxv = max(all_v);
new_v = linspace(minv, maxv, new_L);    %equally spaced values between the min and max
new_y1 = interp1(v1, y1, new_v);
new_y2 = interp1(v2, y2, new_v);
new_y3 = interp1(v3, y3, new_v);
combined_y = vertcat(new_y1(:), new_y2(:), new_y3(:));
plot(new_v, combined_y)

[Giovanni]

Yeah i know i have to make my vectors the same dimension, but how do i do this? How will i crop all my vectors to the min number of rows of one vector? I really have no idea man, I am not being lazy

[Giovanni]

oh and if you are not going to help, may you please stop flagging my questions?? maybe someone else is willing to help me