# automatically filling a matrix

7 views (last 30 days)
bus14 on 22 May 2019
Edited: Stephen23 on 9 Aug 2019
Hi community,
n=200;
i=3;
j=6;
I want to create a matrix which fills a matrix of (n*j) x j and has in the first column -1 for the first n numbers and the rest zeros and for the second column n zeros,n -ones and for the rest zeros again.
I created one manually for the following situation of n=200;i=3;j=6; However, I want to create a script in which I can increase the values of n,i,j and Matlab automatically generates a new correct matrix. Does anyone know how to do this?
My own code is
% when n=200; i=3; and j=6;
AX1= [-ones(n,1);zeros(5*n,1)];
AX2= [zeros(n,1);-ones(n,1);zeros(4*n,1)];
AX3= [zeros(2*n,1);-ones(n,1);zeros(3*n,1)];
AX4= [zeros(3*n,1);-ones(n,1);zeros(2*n,1)];
AX5= [zeros(4*n,1);-ones(n,1);zeros(n,1)];
AX6= [zeros(5*n,1);-ones(n,1)];
AX=[AX1,AX2,AX3,AX4,AX5,AX6];

Stephen23 on 22 May 2019
Edited: Stephen23 on 9 Aug 2019
Method one: eye and kron:
>> n = 5;
>> j = 6;
>> M = kron(-eye(j),ones(n,1))
M =
-1 0 0 0 0 0
-1 0 0 0 0 0
-1 0 0 0 0 0
-1 0 0 0 0 0
-1 0 0 0 0 0
0 -1 0 0 0 0
0 -1 0 0 0 0
0 -1 0 0 0 0
0 -1 0 0 0 0
0 -1 0 0 0 0
0 0 -1 0 0 0
0 0 -1 0 0 0
0 0 -1 0 0 0
0 0 -1 0 0 0
0 0 -1 0 0 0
0 0 0 -1 0 0
0 0 0 -1 0 0
0 0 0 -1 0 0
0 0 0 -1 0 0
0 0 0 -1 0 0
0 0 0 0 -1 0
0 0 0 0 -1 0
0 0 0 0 -1 0
0 0 0 0 -1 0
0 0 0 0 -1 0
0 0 0 0 0 -1
0 0 0 0 0 -1
0 0 0 0 0 -1
0 0 0 0 0 -1
0 0 0 0 0 -1
Method two: eye and repelem:
>> M = repelem(-eye(j),n,1)
M =
-1 0 0 0 0 0
-1 0 0 0 0 0
-1 0 0 0 0 0
-1 0 0 0 0 0
-1 0 0 0 0 0
0 -1 0 0 0 0
0 -1 0 0 0 0
0 -1 0 0 0 0
0 -1 0 0 0 0
0 -1 0 0 0 0
0 0 -1 0 0 0
0 0 -1 0 0 0
0 0 -1 0 0 0
0 0 -1 0 0 0
0 0 -1 0 0 0
0 0 0 -1 0 0
0 0 0 -1 0 0
0 0 0 -1 0 0
0 0 0 -1 0 0
0 0 0 -1 0 0
0 0 0 0 -1 0
0 0 0 0 -1 0
0 0 0 0 -1 0
0 0 0 0 -1 0
0 0 0 0 -1 0
0 0 0 0 0 -1
0 0 0 0 0 -1
0 0 0 0 0 -1
0 0 0 0 0 -1
0 0 0 0 0 -1
Method three: blkdiag and a comma separated list:
>> C = {-ones(n,1)};
>> M = blkdiag(C{ones(1,j)})
M =
-1 0 0 0 0 0
-1 0 0 0 0 0
-1 0 0 0 0 0
-1 0 0 0 0 0
-1 0 0 0 0 0
0 -1 0 0 0 0
0 -1 0 0 0 0
0 -1 0 0 0 0
0 -1 0 0 0 0
0 -1 0 0 0 0
0 0 -1 0 0 0
0 0 -1 0 0 0
0 0 -1 0 0 0
0 0 -1 0 0 0
0 0 -1 0 0 0
0 0 0 -1 0 0
0 0 0 -1 0 0
0 0 0 -1 0 0
0 0 0 -1 0 0
0 0 0 -1 0 0
0 0 0 0 -1 0
0 0 0 0 -1 0
0 0 0 0 -1 0
0 0 0 0 -1 0
0 0 0 0 -1 0
0 0 0 0 0 -1
0 0 0 0 0 -1
0 0 0 0 0 -1
0 0 0 0 0 -1
0 0 0 0 0 -1
bus14 on 22 May 2019