ctr_gram controllability gramian

## Syntax

                Gc = ctr_gram(sl)
                Gc = ctr_gram(A, B)
                Gc = ctr_gram(A, B, dom)

## Arguments

A,B

  two real matrices of appropriate dimensions

dom

  character string (`'c'` (default value) or `'d'`)

sl

  linear system, `syslin` list

## Description

Controllability gramian of `(A,B)` or `sl` (a `syslin` linear system).

`dom` character string giving the time domain : `"d"` for a discrete time system and `"c"` for continuous time (default case).

## Examples

    A=diag([-1,-2,-3]);B=rand(3,2);
    Wc=ctr_gram(A,B)
    U=rand(3,3);A1=U*A/U;B1=U*B;
    Wc1=ctr_gram(A1,B1)    //Not invariant!

## See also

- equil1
- obs_gram
- contr
- cont_mat
- cont_frm
- contrss