MATLAB Function Reference Volume 1: A - E - Bad Request

2diag
Purpose Diagonal matrices and diagonals of a matrix
Syntax X = diag(v,k)
X = diag(v)
v = diag(X,k)
v = diag(X)
Description X = diag(v,k) when v is a vector of n components, returns a square matrix X
of order n+abs(k), with the elements of v on the kth diagonal. k = 0represents
the main diagonal, k > 0 above the main diagonal, and k < 0 below the main
diagonal.
k = 0
k < 0
X = diag(v) puts v on the main diagonal, same as above with k=0.
v = diag(X,k) for matrix X, returns a column vector v formed from the
elements of the kth diagonal of X.
v = diag(X) returns the main diagonal of X, same as above with k=0.
Examples diag(diag(X)) is a diagonal matrix.
sum(diag(X)) is the trace of X.
The statement
k > 0
diag(-m:m)+diag(ones(2*m,1),1)+diag(ones(2*m,1),-1)
produces a tridiagonal matrix of order 2*m+1.
diag
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