diag (Symbolic Math Toolbox)

Create or extract symbolic diagonals

Syntax

```
diag(A,k)
diag(A)
```

Description

diag(A,k), where A is a row or column vector with n components, returns a square symbolic matrix of order n+abs(k), with the elements of A on the k-th diagonal. k = 0 signifies the main diagonal; k > 0, the k-th diagonal above the main diagonal; k < 0, the k-th diagonal below the main diagonal.

diag(A,k), where A is a square symbolic matrix, returns a column vector formed from the elements of the k-th diagonal of A.

diag(A), where A is a vector with n components, returns an n-by-n diagonal matrix having A as its main diagonal.

diag(A), where A is a square symbolic matrix, returns the main diagonal of A.

Examples

Suppose

```
v = [a b c]
```

Then both diag(v) and diag(v,0) return

```
[ a, 0, 0 ]
[ 0, b, 0 ]
[ 0, 0, c ]
```

diag(v,-2) returns

[ 0, 0, 0, 0, 0]
[ 0, 0, 0, 0, 0]
[ a, 0, 0, 0, 0]
[ 0, b, 0, 0, 0]
[ 0, 0, c, 0, 0]

Suppose

A =
    [ a, b, c ]
    [ 1, 2, 3 ]
    [ x, y, z ]

diag(A) returns

```
[ a ]
[ 2 ]
[ z ]
```

diag(A,1) returns

```
[ b ]
[ 3 ]
```

See Also

tril, triu

det diff