MATLAB: Add elements to a matrix

matrixrepelem to repeat elements

Hello.

I have the following problem: I have a matrix A (3×3), and I want to add elements to this matrix and create table B with dimensions 6×6. More specifically, I want the new data to be the same as the original ones.

A=(1 2 3; 4 5 6; 7 8 9)
% A=(1 2 3
%    4 5 6
%    7 8 9)
B=(1 1 2 2 3 3; 4 4 5 5 6 6; 7 7 8 8 9 9)
% B=( 1 1 2 2 3 3
%     4 4 5 5 6 6
%     7 7 8 8 9 9)

That is, the first element of table A (1,1) is 1. Then, in positions (1,1) (1,2) of the new matrix (B) it must again be 1. In position A (1,2) it is 2, then in positions (1,3) and (1,4) of B to appear 2. Respectively with the other elements. How is this done? Your help is important.

Best Answer

Use repelem()

A = [1 2 3; 4 5 6; 7 8 9]
B = repelem(A, 1, 2)

Note: In MATLAB [ ] are used to create arrays.

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Start with "If an entry in B is greater than or equal to zero": You can either run a loop over all elements of B or use "logical indexing":

% Linear indexing:
for k = 1:numel(B)
   if B(k) >= 0
     ...
   end
end

Or two indices for rows and columns:

for r = 1:size(B, 2)
  for c = 1:size(B, 1)
    if B(r, c) >= 0
       ...
    end
  end
end

Or "logical indexing":

index = (B >= 0);
disp(B(index))

Now try to use this to modify B. Use the mentioned terms to search in the documentation and in the internet.

Best Answer

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