des2ss descriptor to state-space

## Syntax

                Sl = des2ss(Des)
                Sl = des2ss(A, B, C, D, E)
                Sl = des2ss(A, B, C, D, E, tol)

## Arguments

A,B,C,D,E

  real matrices of appropriate dimensions

Des

  list

Sl

  `syslin` list

tol

  real parameter (threshold) (default value `100*%eps`).

## Description

Descriptor to state-space transform.

`Sl=des2ss(A,B,C,D,E)` returns a linear system `Sl` equivalent to the descriptor system `(E,A,B,C,D)`.

For index one `(E,A)` pencil, explicit formula is used and for higher index pencils `rowshuff` is used.

`Sl=des2ss(Des)` with `Des=list('des',A,B,C,D,E)` returns a linear system `Sl` in state-space form with possibly a polynomial `D` matrix.

A generalized Leverrier algorithm is used.

## Examples

    s=poly(0,'s');G=[1/(s-1),s;1,2/s^3];
    S1=tf2des(G);S2=tf2des(G,"withD");
    W1=des2ss(S1);W2=des2ss(S2);
    clean(ss2tf(W1))
    clean(ss2tf(W2))

## See also

- des2tf
- glever
- rowshuff