I want to make an identity matrix

i want to make a matrix that look like this

How could i achieve this efficiently .Thanks in advace

Answer 1

[the cyclist]

I've made some assumptions about the pattern, but I expect it is what you want.

This should be highly efficient. The algorithm is a bit obfuscated.

% Input 
N = 4;

% Start with all 0s
M = zeros(N,N*(N+1));

% Fill in the 1s
M(1:N*N+1:end-N*N) = 1;

% Fill in the -1s
M(:,N*N+1) = -1;

% Display the result
disp(M)

     1     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0    -1     0     0     0
     0     0     0     0     1     0     0     0     0     0     0     0     0     0     0     0    -1     0     0     0
     0     0     0     0     0     0     0     0     1     0     0     0     0     0     0     0    -1     0     0     0
     0     0     0     0     0     0     0     0     0     0     0     0     1     0     0     0    -1     0     0     0

Answer 2

[John D'Errico]

These are starting to look like homework questions.

Did you not read the answer to the last question you asked? You could not use that idea to build this matrix?

A = kron([eye(4),zeros(4,1)],[1 0 0 0])

A = 4×20

1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0

That gets you almost there, with the first 16 columns correct, and a total of 20 columns. Then it would be simple enough to stuff in the -1 elements in column 17.

A(:,17) = -1

A = 4×20

1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 -1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 -1 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 -1 0 0 0

spy(A)