bugGNU Octave - Bugs: bug #52608, quiver/quiver3 marker...

 
 

bug #52608: quiver/quiver3 marker documentation is unclear

Submitter:  None
Submitted:  Thu 07 Dec 2017 01:13:48 AM UTC
   
 
Category:  Documentation Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Documentation
Status:  Fixed Assigned to:  None
Originator Name:  Originator Email:  -email is unavailable-
Open/Closed:  * Closed Release:  * 4.2.1
Operating System:  * GNU/Linux Fixed Release:  None
Planned Release:  None
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Thu 07 Dec 2017 06:01:26 PM UTC, comment #7: 

I tried to make the documentation clearer in this cset: http://hg.savannah.gnu.org/hgweb/octave/rev/6915cc404dba.

In addition, this revealed a bug with processing a linestyle argument, so I fixed that as well in this cset http://hg.savannah.gnu.org/hgweb/octave/rev/b71ba49473f4.

Marking as fixed and closing report.

Rik <rik5>
Group administrator
Thu 07 Dec 2017 04:38:44 PM UTC, comment #6: 

Thanks Markus.  Richard Crozier also answered my request for help on the Octave Maintainer's list.  Attached is the picture he got.  The markers are drawn at the origin of the arrows which is equivalent to saying the "base of the arrowshafts" or "the points defined by X, Y inputs".


Rik <rik5>
Group administrator
Thu 07 Dec 2017 08:35:32 AM UTC, comment #5: 

I ran the code from comment #2 on Matlab R2016a: It doesn't show arrow heads. Just the red marker at the bases of the vector (first two arguments) and red lines.

Markus Mützel <mmuetzel>
Group administrator
Thu 07 Dec 2017 04:22:18 AM UTC, comment #4: 

And I have no simple idea how to rephrase the documentation.

Maybe change this sentence
"If a marker is specified then markers at the grid points of the vectors are drawn rather than arrows."
to
"If a marker is specified then additional markers at the grid points of the vectors are drawn."
?

But it also depends on whether the arrowhead should also be drawn in this case.

Anonymous
Thu 07 Dec 2017 03:58:31 AM UTC, comment #3: 

Oh, I'm not a native English speaker, so I'm afraid that I could not help to give good documentation.

I do not use Matlab.  I only use GNU Octave, which is my favorite software.

Anonymous
Thu 07 Dec 2017 02:25:12 AM UTC, comment #2: 

Actually, if you have access to Matlab, could you run this test code


quiver(1:2,3:4, -2:-1,1:2, 'r-o')


It is not clear from their documentation what happens when there is a marker specified.  Does it mean the arrowhead isn't drawn?

Rik <rik5>
Group administrator
Thu 07 Dec 2017 02:15:36 AM UTC, comment #1: 

Maybe the documentation should be clearer.  Octave is Matlab-compatible and Matlab says


quiver(...,LineSpec) specifies line style, marker symbol, and color using any valid LineSpec. quiver draws the markers at the origin of the vectors.


In other words, the markers SHOULD be at the grid points or origin of the vectors.

Can you think of a could way to rephrase the documentation?

Rik <rik5>
Group administrator
Thu 07 Dec 2017 01:13:48 AM UTC, original submission:  

If no marker is specified, then the arrows are at the head of the vectors. For example,

quiver(1:2,3:4, -2:-1,1:2)
quiver(1:2,3:4, -2:-1,1:2, 'r')
quiver(1:2,3:4, -2:-1,1:2, 'b--')
quiver3(1:2,3:4,5:6, -2:-1,1:2,0:1)
quiver3(1:2,3:4,5:6, -2:-1,1:2,0:1, 'r')
quiver3(1:2,3:4,5:6, -2:-1,1:2,0:1, 'b--')


But if a marker is specified, then the markers are at the tail of the vectors. For example,

quiver(1:2,3:4, -2:-1,1:2, 'r-v')
quiver(1:2,3:4, -2:-1,1:2, 'b--o')
quiver(1:2,3:4, -2:-1,1:2, 'b-o','filled')
quiver3(1:2,3:4,5:6, -2:-1,1:2,0:1, 'r-v')
quiver3(1:2,3:4,5:6, -2:-1,1:2,0:1, 'b--o')
quiver3(1:2,3:4,5:6, -2:-1,1:2,0:1, 'b-o','filled')



The docstring of quiver/quiver3 says that

The style to use for the plot can be defined with a line style
STYLE of the same format as the 'plot' command.  If a marker is
specified then markers at the grid points of the vectors are drawn
rather than arrows.  If the argument "filled" is given then the
markers are filled.


In this above paragraph, what does "the grid points of the vectors" mean?  Does it mean the head or the tail of the vectors?

Anonymous

 

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file #42598:  quiver_test.png added by rik5 (9KiB - image/png)

 

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    Follow 7 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2017-12-07 rik5 StatusConfirmed Fixed
        Open/ClosedOpen Closed
    2017-12-07 rik5 Attached File- Added quiver_test.png, #42598
    2017-12-07 rik5 CategoryPlotting Documentation
        Item GroupIncorrect Result Documentation
        StatusNone Confirmed
        Summaryquiver/quiver3 marker at the tail rather than at the head quiver/quiver3 marker documentation is unclear

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