[Octave-bug-tracker] [bug #63661] Results of function "tf" may lead to execution error / Other inconstencies

[Charles Praplan]

URL:
  <https://savannah.gnu.org/bugs/?63661>

                 Summary: Results of function "tf" may lead to execution error
/ Other inconstencies
                 Project: GNU Octave
               Submitter: charprap
               Submitted: Sat 14 Jan 2023 10:17:10 AM UTC
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Charles Praplan
        Originator Email: 
             Open/Closed: Open
                 Release: 7.3.0
         Discussion Lock: Any
        Operating System: Microsoft Windows
           Fixed Release: None
         Planned Release: None


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Follow-up Comments:


-------------------------------------------------------
Date: Sat 14 Jan 2023 10:17:10 AM UTC By: Charles Praplan <charprap>
1)
Everything started with the following code which was working but now produces
an error:

sig=[0:9]; t=[0:9]; sys_c=tf(2,1); lsim(sys_c,sig,t,'b');
error: c2d: system is already discrete-time


Note that tf is called with the arguments to generate a continuous system:
sys_c.
sys_c is newly generated as being both a continuous and a discrete static gain
(previously Continuous-time model).
This is ok and is the same in matlab.

The error occurs when passing sys_c to c2d which does not accept to handle
sys_c because it is already discrete.

The origin of this is in the function __adjust_tf_data__.m which has been
modified (the solution is perhaps in the fct c2d).

Other inconstencies :

2) sys=tf(2,1) and sys=tf([0 2],[0 1]) do not produce the same result:


sys=tf(2,1)
isct(sys), isdt(sys), sys.Ts
sys=tf([0 2],[0 1]),
isct(sys), isdt(sys), sys.Ts



3) Following call results in the lost of sampling time information:

sys_1d=tf(2,1,7);
sys_1d.Ts










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