diag(1)

NAME
diag - diagonal including or extracting

CALLING SEQUENCE
[y]=diag(vm, [k])

PARAMETERS

vm  : vector or matrix

k   : integer (default value 0)

y   : vector or matrix

DESCRIPTION
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.

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,...).

EXAMPLE
diag(-m:m) +  diag(ones(2*m,1),1) +diag(ones(2*m,1),-1)
gives a tri-diagonal matrix of order 2*m+1

SEE ALSO
sysdiag