[Octave-bug-tracker] [bug #65091] [octave forge] (nurbs) nrbderiv outputs nurbs with zero weight.

[Liang Tang]

URL:
  <https://savannah.gnu.org/bugs/?65091>

                 Summary:  [octave forge] (nurbs) nrbderiv outputs nurbs with
zero weight.  
                   Group: GNU Octave
               Submitter: lt1234
               Submitted: Thu 28 Dec 2023 10:40:19 PM UTC
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: lt1234
        Originator Email: 
             Open/Closed: Open
                 Release: 8.2.0
         Discussion Lock: Any
        Operating System: Microsoft Windows
           Fixed Release: None
         Planned Release: None


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Follow-up Comments:


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Date: Thu 28 Dec 2023 10:40:19 PM UTC By: Liang Tang <lt1234>
nrbderiv resets the nurbs weight to zero in build-in bspderiv. nrbkntplot
would not plot a nurbs with zero weights. Please see the attached ofig. 
Thanks.  

pkg load nurbs
Q=[0, 0; 3,4;-1,4;-4,0;-4,-3]
p=3; % cubic 
%
P=[0        0; ...
   7.3170   3.6868; ...
  -2.9581   6.6783; ...
  -4.4950  -0.6737; ...
  -4.0000  -3.0000]; 
U=[0        0        0        0   0.5490   1.0000   1.0000   1.0000   1.0000];

nurbs   = nrbmak(cp=P',knots=U);
nurbs_d = nrbderiv (nurbs);nurbs_d.coefs  % zero weight 

figure('name', 'nrbderiv weight=0');
 
subplot(1,2,1); % no plot
nrbkntplot(nurbs_d);   

subplot(1,2,2); % plot
nurbs_d.coefs(4,:)=[1 1 1 1]; 
nrbkntplot(nurbs_d);






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File Attachments:


-------------------------------------------------------
Date: Thu 28 Dec 2023 10:40:19 PM UTC  Name: nrbkntplot.ofig  Size: 91KiB  
By: lt1234

<http://savannah.gnu.org/bugs/download.php?file_id=55486>

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