[Octave-bug-tracker] [bug #42763] Change in behaviour of interp1 function breaks signal processing functions such as fir1

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?42763>

                 Summary: Change in behaviour of interp1 function breaks
signal processing functions such as fir1
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Sun 13 Jul 2014 03:03:31 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Regression
                  Status: None
             Assigned to: None
         Originator Name: Robert Jackson
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.8.1
        Operating System: GNU/Linux

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Details:

The fir1 function from the signal package generates incorrect results in
Octave 3.8.1 compared to Octave 3.6.4 (and Matlab).  I've tracked the mismatch
down to the interp1 function (which is built-in I believe).

Below is the output of my fir1 testcase.  Below that is the output of the
interp1 function (which is called by fir2 - which is itself called from
fir1).

GNU Octave, version 3.6.4

octave:1> fir1(32,0.2)'
ans =

  -8.7001e-04
   8.6629e-05
   1.6246e-03
   3.7088e-03
   5.3433e-03
   4.6062e-03
  -3.5509e-04
  -9.7044e-03
  -2.0575e-02
  -2.7019e-02
  -2.1744e-02
   7.7639e-04
   4.1127e-02
   9.3305e-02
   1.4568e-01
   1.8455e-01
   1.9891e-01
   1.8455e-01
   1.4568e-01
   9.3305e-02
   4.1127e-02
   7.7639e-04
  -2.1744e-02
  -2.7019e-02
  -2.0575e-02
  -9.7044e-03
  -3.5509e-04
   4.6062e-03
   5.3433e-03
   3.7088e-03
   1.6246e-03
   8.6629e-05
  -8.7001e-04


GNU Octave, version 3.8.1

octave:1> fir1(32,0.2)'
ans =

   3.4685e-04
   4.8446e-04
   6.5126e-04
   7.4865e-04
   6.3247e-04
   2.7611e-04
   1.0088e-06
   6.5234e-04
   3.5772e-03
   1.0320e-02
   2.2070e-02
   3.9039e-02
   6.0007e-02
   8.2297e-02
   1.0225e-01
   1.1611e-01
   1.2108e-01
   1.1611e-01
   1.0225e-01
   8.2297e-02
   6.0007e-02
   3.9039e-02
   2.2070e-02
   1.0320e-02
   3.5772e-03
   6.5234e-04
   1.0088e-06
   2.7611e-04
   6.3247e-04
   7.4865e-04
   6.5126e-04
   4.8446e-04
   3.4685e-04



GNU Octave, version 3.6.4

octave:1> m = interp1([0;0.2;0.2;1], [1;1;0;0], [0.00000 0.19805 0.20000
0.20195 1.00000])
m =

   1   1   0   0   0


GNU Octave, version 3.8.1

octave:1> m = interp1([0;0.2;0.2;1], [1;1;0;0], [0.00000 0.19805 0.20000
0.20195 1.00000])
m =

   1.00000   0.00975   0.00000   0.00000   0.00000


Note m(2) is completely different.

Please let me know if you require further information

Regards
Robert




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