Convenient matrix building functions are
eye(10) identity matrix zeros(10) matrix of zeros ones(10) matrix of ones diag(A) returns diagonal M.E. as vector triu(A) upper triangular part of a matrix tril(A) lower triangular part of a matrix rand(10) randomly generated matrix hilb(5) Hilbert matrix magic(5) magic square toeplitz see help toeplitzFor example, zeros(m,n) produces an m-by-n matrix of zeros and zeros(n) produces an n-by-n one; if A is a matrix, then zeros(A) produces a matrix of zeros of the same size as A .
If x is a vector, diag(x) is the diagonal matrix with x down the diagonal; if A is a square matrix, then diag(A) is a vector consisting of the diagonal of A . What is diag(diag(A))? Try it.
Matrices can be built from blocks. For example, if A is a 3-by-3 matrix, then
B = [A, zeros(3,2); zeros(2,3), eye(2)]will build a certain 5-by-5 matrix. Try it.