abcd state-space matrices

## Syntax

    [A,B,C,D] = abcd(sl)

## Arguments

sl

  linear system (`syslin` list) in state-space or transfer form

A,B,C,D

  real matrices of appropriate dimensions

## Description

returns the `A,B,C,D` matrices from a linear system `Sl`.

Utility function. For transfer matrices `Sl` is converted into state-space form by `tf2ss`.

The matrices `A,B,C,D` are the elements `2` to `5` of the `syslin` list `Sl`, i.e. `[A,B,C,D] = Sl(2:5)` .

## Examples

    A=diag([1,2,3]);B=[1;1;1];C=[2,2,2];
    sys=syslin('c',A,B,C);
    sys("A")
    sys("C")
    [A1,B1,C1,D1]=abcd(sys);
    A1
    systf=ss2tf(sys);
    [a,b,c,d]=abcd(systf)
    spec(a)
    c*b-C*B
    c*a*b-C*A*B

## See also

- syslin
- ssrand