# Add elements to a matrix

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stelios loizidis on 30 Dec 2020
Commented: stelios loizidis on 30 Dec 2020
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.

Ameer Hamza on 30 Dec 2020
Edited: Ameer Hamza on 30 Dec 2020
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.
Ameer Hamza on 30 Dec 2020
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 on 30 Dec 2020
It works. Thank you very much!!!!