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How to create a specific diagonal Matrix

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Stefano Di Vito
Stefano Di Vito 2018-4-20
评论： Stephen23 2018-4-20
Hi everyone! I'm trying to find the way to write a generic code to obtain a matrix like the one in this example:
if true
A=[1 1 1 0 0 0 0 0 0;0 0 0 1 1 1 0 0 0;0 0 0 0 0 0 1 1 1]
end
To be clearer, i need a code to fill my matrix, which dimension is (T,T^2). In the example i have T=3. I need the general code because i need a matrix for each T i set, and it should respect the criteria of the example. This means that i have, for each row, a ones(1,T) vector that starts when the ones vector of the previous row ends. The first row should start with a ones(1,T) vector, as in the example. It is a sort of diagonal matrix i guess. I need it because it is part of the unequality constraints matrix in a linear program i'm developing. Hope someone could help me! thanks a lot in advance!

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回答（2 个）

Birdman
Birdman 2018-4-20

Try this:

T=3;
for i=1:T
    A(i,:)=circshift([ones(1,T) zeros(1,T^2-T)],T*(i-1));
end
Stephen23
Stephen23 2018-4-20
编辑：Stephen23 2018-4-20

That is exactly what blkdiag is for:

>> V = [1,1,1];
>> blkdiag(V,V,V)
ans =
   1   1   1   0   0   0   0   0   0
   0   0   0   1   1   1   0   0   0
   0   0   0   0   0   0   1   1   1

This is much simpler and much more efficient than trying to write your own code using loops. Remember that MATLAB is a high-level language, so loops are often not the best solution.

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