lin linearization

## Syntax

                sl = lin(sim,x0,u0)
                [A,B,C,D] = lin(sim, x0, u0)

## Arguments

sim

  function

x0, u0

  vectors of compatible dimensions

A,B,C,D

  real matrices

sl

  `syslin` list

## Description

linearization of the non-linear system `[y,xdot]=sim(x,u)` around `x0,u0`.

`sim` is a function which computes `y` and `xdot`.

The output is a linear system (`syslin` list) `sl` or the four matrices `(A,B,C,D)`

For example, if `ftz` is the function passed to ode e.g.

    [zd]=ftz(t,z,u)

and if we assume that `y=x`

`[z]=ode(x0,t0,tf,list(ftz,u)` compute `x(tf)`.

If `simula` is the following function:

    deff('[y,xd]=simula(x,u)','xd=ftz(tf,x,u); y=x;');

the tangent linear system `sl` can be obtained by:

    [A,B,C,D]=lin(simula,z,u)
    sl = syslin('c',A,B,C,D,x0)

## Examples

    deff('[y,xdot]=sim(x,u)','xdot=[u*sin(x);-u*x^2];y=xdot(1)+xdot(2)')
    sl=lin(sim,1,2);

## See also

- external
- derivat