Hi,
I have tried to create a discrete feedback system with the control package 
(1.0.11 with octave 3.0.1), but got unexpected results.

I create the system with:

sysUNIT = tf(1, 1, 1);
sysB1 = tf([8e-9 -5.6e-9], [1 -1], 1);
sysB2 = tf([125e6], [1 -1], 1);
sysB3 = sysmult(sysB1, sysB2);
sysCL2 = feedback(sysUNIT, sysB3);
sysout(sysCL2, 'tf');

The resulting transfer function is

1*z^2 - 2*z^1 + 0.20215
-----------------------
1*z^2 - 1*z^1 + 0.3

However, the correct result should be

1*z^2 - 2*z^1 + 1
-----------------------
1*z^2 - 1*z^1 + 0.3

When I do not use the sysmult function but do the multiplication of sysB1 and 
sysB2 by myself, I get the correct result:

sysA1 = tf([1 -.7], [1 -2 1], 1);
sysCL = feedback(sysUNIT, sysA1);
sysout(sysCL, 'tf');

1*z^2 - 2*z^1 + 1
-------------------
1*z^2 - 1*z^1 + 0.3

Am I doing something wrong here? Do you get the same results?

I got several warnings from the sysgroup command during the execution of this 
script, e.g.
warning: sysgroup:     changed output name 2 to y_1_2
should I take these serious?

Thank you, best regards,
Christian




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