21.1.1 Creating Diagonal Matrices

The most common and easiest way to create a diagonal matrix is using the built-in function diag. The expression diag (v), with v a vector, will create a square diagonal matrix with elements on the main diagonal given by the elements of v, and size equal to the length of v. diag (v, m, n) can be used to construct a rectangular diagonal matrix. The result of these expressions will be a special diagonal matrix object, rather than a general matrix object.

Diagonal matrix with unit elements can be created using eye. Some other built-in functions can also return diagonal matrices. Examples include balance or inv.

Example:

diag (1:4)
⇒
Diagonal Matrix

   1   0   0   0
   0   2   0   0
   0   0   3   0
   0   0   0   4

  diag (1:3,5,3)

⇒
Diagonal Matrix

   1   0   0
   0   2   0
   0   0   3
   0   0   0
   0   0   0