Add elements to a matrix

Hello.

I have the following problem: I have a matrix A (3x3), and I want to add elements to this matrix and create table B with dimensions 6x6. 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.

Answer 1

[Ameer Hamza]

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.

[stelios loizidis]

One more question. If based on the data in matrix A I want to make an matrix C (6X6) that has the following elements:

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

How is this done?

[Ameer Hamza]

Try this

A = [1 2 3; 4 5 6; 7 8 9]
B = repelem(A, 1, 2)
C = B.*repmat([1 -1], size(A))

[Steven Lord]

A = [1 2 3; 4 5 6; 7 8 9]

A = 3×3

1 2 3 4 5 6 7 8 9

●

B = kron(A, [1 -1])

B = 3×6

1 -1 2 -2 3 -3 4 -4 5 -5 6 -6 7 -7 8 -8 9 -9

●

[stelios loizidis]

I tried the C = B.*repmat([1 -1], size(A)). But I have the following issue now. when I want to create the matrix D

% D=(1 1 -1 -1 2 2 -2 -2 3 3 -3 -3
%    4 4 -4 -4 5 5 -5 -5 6 6 -6 -6
%    7 7 -7 -7 8 8 -8 -8 9 9 -9 -9)

I use this: D = B.*repmat([1 -1], size(A)), but the following error occurs: "Matrix dimensions must agree".

[Ameer Hamza]

In this case, try

A = [1 2 3; 4 5 6; 7 8 9]
B = repelem(A, 1, 4)
D = B.*repmat([1 1 -1 -1], size(A))

or as Steven mentioned,

A = [1 2 3; 4 5 6; 7 8 9]
D = kron(A, [1 1 -1 -1])

[stelios loizidis]

It works. Thank you very much!!!!