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# Matrix building functions

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 toeplitz```
For 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.