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ROOKIE Q: Using ltitr() + possible bug

From: Iñaky Pérez González
Subject: ROOKIE Q: Using ltitr() + possible bug
Date: Tue, 21 Oct 1997 23:40:53 +0200


        I'm new to Octave, as I have started this year with a class
which uses matlab, and I'm trying to do it with Octave. Yaw ... love
free software, you know.

        Well, everything went fine until I tried to use a function
which came along with the control package of Matlab, that we need to
use. I pretended to use the impulse() function to feed the input of a
lineal control system, but it was requesting a function, ltitr() which
octave, AFAIK, doesn't have, and MatLab has it built-in as an in-core
one, so no source available (even in the front package, which was said
to have more stuff).

        So, following a tip for =D3scar M=E1rquez, I implemented the
function using this:

function _x =3D ltitr (_a, _b, _u, _x0)

_n =3D length (_u);
_U =3D _u';

for _i=3D1:_n
        _x(:,_i) =3D _x0;
        _x0 =3D _a * _x0 + _b * _U(:, _i);
_x =3D _x.';

(shameless copy from MatLab's help).

        Then everything seemed to be fine until I had to use the
ss2tf() function from the MatLab control package. It gives far away
the results it gives in MatLab. Haven't seen a possible cause ???

        I attach the file which causes the problem. Look at the
ss2tf() function call. It returns two matrixs, num_chk and
den_chk. They should be equal to num and den, and they do not. Anybody
could tell me if it is a bug or a feature? and if it is a feature,
what am I doing wrong?


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