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[Octave-bug-tracker] [bug #38528] Function ellipord outputs complex filt


From: anonymous
Subject: [Octave-bug-tracker] [bug #38528] Function ellipord outputs complex filter order for high-pass filter
Date: Sat, 16 Mar 2013 13:58:35 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/535.19 (KHTML, like Gecko) Ubuntu/11.04 Chromium/18.0.1025.151 Chrome/18.0.1025.151 Safari/535.19

URL:
  <http://savannah.gnu.org/bugs/?38528>

                 Summary: Function ellipord outputs complex filter order for
high-pass filter
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Sat 16 Mar 2013 01:58:34 PM UTC
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.2.4
        Operating System: GNU/Linux

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Details:

When using the function ellipord to calculate the order of a high-pass* Cauer
filter, it returns a complex number whereas the order of a filter should
always be a real and positive integer. The following line reproduces the
issue:

>> ellipord(0.955,0.945,1,20)
output: ans = 4 - 2i

Based on order calculations of bandpass filters and a lowpass filter with the
same distance between the passband an the stopband, maximum passband
attenuation and minimum stopband attenuation, an order of 3 or 4 is expected.
A file with all calculated filters is attached.

*High-pass filter: a filter with only one passband edge and one stopband edge
with the passband edge at a higher frequency than the stopband edge. In other
words, all frequencies beneath the stopband edge are suppressed and all
frequencies above the passband edge are preserved.




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File Attachments:


-------------------------------------------------------
Date: Sat 16 Mar 2013 01:58:34 PM UTC  Name: reproduce_ellipord_bug.m  Size:
1kB   By: None

<http://savannah.gnu.org/bugs/download.php?file_id=27612>

    _______________________________________________________

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  <http://savannah.gnu.org/bugs/?38528>

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