diag - diagonal including or extracting
for vm a (row or column) n-vector diag(vm) returns a diagonal matrix with entries of vm along the main diagonal.
diag(vm,k) is a (n+abs(k))x(n+abs(k)) matrix with the entries of vm along the kth diagonal. k=0 is the main diagonal k>0 is for upper diagonals and k<0 for lower diagonals.
For a matrix vm , diag(vm,k) is the column vector made of entries of the kth diagonal of vm . diag(vm) is the main diagonal of vm . diag(diag(x)) is a diagonal matrix.
If vm is a sparse matrix diag(vm,k) returns a sparse matrix.
To construct a diagonal linear system, use sysdiag .
Note that eye(A).*A returns a diagonal matrix made with the diagonal entries of A . This is valid for any matrix (constant, polynomial, rational, state-space linear system,...).
diag([1,2]) A=[1,2;3,4]; diag(A) // main diagonal diag(A,1) diag(sparse(1:10)) // sparse diagonal matrix // form a tridiagonal matrix of size 2*m+1 m=5;diag(-m:m) + diag(ones(2*m,1),1) +diag(ones(2*m,1),-1)