[Octave-bug-tracker] [bug #52254] filtic output not compatible with MATLAB

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?52254>

                 Summary: filtic output not compatible with MATLAB
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Thu 19 Oct 2017 07:01:38 PM UTC
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  Status: None
             Assigned to: None
         Originator Name: Tony Richardson
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.2.1
        Operating System: Microsoft Windows

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Details:

I was getting incorrect results using the filter function.  I tracked the
issue down to a problem with filtic.

b = [4 -3]; a = [2 -3 1];
filtic(b, a, [0 1])

returns [-1 0] as a result.  The correct result (and that returned by MATLAB)
is [-0.5 0].

Octave returns the MATLAB result if I divide both b and a by a(1):

b = [4 -3]; a = [2 -3 1];
filtic(b/a(1), a/a(1), [0 1])

gives [-0.5 0]. 

An easy fix is to divide both vectors by a(1) inside the filtic function, but
I am not sure that is the best solution.






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