How to convert a matrix into a 3d matrix
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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???
3 个评论
sixwwwwww
2013-12-11
do you just want to replicate it N times?
Jos (10584)
2013-12-11
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
2013-12-11
Do you mean "a function" instead of "a vector"???
采纳的回答
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!
更多回答（3 个）
Image Analyst
2013-12-11
编辑：Image Analyst
2013-12-11
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
5 个评论
Giovanni
2013-12-11
Image Analyst
2013-12-11
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
2013-12-11
Giovanni
2013-12-11
Image Analyst
2013-12-11
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
Walter Roberson
2013-12-12
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)
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