# empty

([]) empty matrix

## Description

`[]` denotes the empty matrix. It is uniquely defined and has 0 row and 0 column, i.e. `size([]) =[0,0]` . The following convenient conventions are made:

`[] * A = A * [] = []`

`[] + A = A + [] = A`

`[ [], A] = [A, []] = A` `inv([]) =[]`

`det([])=cond([])=rcond([])=1, rank([])=0`

Matrix functions return `[]` or an error message when there is no obvious answer. Empty linear systems (`syslin` lists) may have several rows or columns.

## Examples

    s=poly(0,'s');
    A = [s, s+1];
    A+[], A*[]
    A=rand(2,2);
    AA=A([],1), size(AA)
    svd([])
    w=ssrand(2,2,2);
    wr=[]*w;
    size(wr), w1=ss2tf(wr), size(w1)

## See Also

- matrices
- poly
- string
- boolean
- rational
- syslin