bugGNU Octave - Bugs: bug #46168, OpenGL use of single causing...

 
 

bug #46168: OpenGL use of single causing problems in errorbar

Submitted by:  José Luis García Pallero <jgpallero>
Submitted on:  Fri 09 Oct 2015 10:04:49 PM UTC  
 
Category:  Plotting with OpenGL Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Incorrect Result
Status:  Postponed Assigned to:  None
Originator Name:  Open/Closed:  Open
Release:  4.0.0 Operating System:  Any

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Fri 09 Oct 2015 11:20:41 PM UTC, comment #1: 

I don't think the problem is errorbar.  I think you're running into the fact that OpenGL uses class single to represent numbers.  If I switch to gnuplot for plotting, which uses doubles to represent numbers, then the plot looks alright.

graphics_toolkit gnuplot
x=[2000.59 2000.60 2000.61];
y=[0.00 2.10 -2.70];
ey=[1.36 2.49 2.79];
errorbar(x,y,ey,'.');
print('test_errorbar.pdf','-dpdf');

It's not the fact that the numbers are close together, it's the fact that you're asking for a precision of .01 / 2000 or 5 parts per million.  An easy way around this is to scale the numbers.  See below.

x=[2000.59 2000.60 2000.61];
x = x - 2000;
y=[0.00 2.10 -2.70];
ey=[1.36 2.49 2.79];
errorbar(x,y,ey,'.');

If you want the plot to actually read correctly you can change the xticklabel property on the axis manually.  Assuming the code above,

set (gca, "xtick", [0.59, 0.60, 0.61]);
set (gca, "xticklabel", {"2000.59", "2000.60", "2000.61"});

Rik <rik5>
Project Administrator
Fri 09 Oct 2015 10:04:49 PM UTC, original submission:  

When I plot this data

x=[2000.59 2000.60 2000.61];
y=[0.00 2.10 -2.70];
ey=[1.36 2.49 2.79];
errorbar(x,y,ey,'.');
print('test_errorbar.pdf','-dpdf');

the obtained plot is inaccurate because the vertical lines do not match the point symbol and also there are problems with the horizontal ticks at the vertical lines extremes. I attach a PDF file with the plot made with my Octave 4.0.0 on Debian.

The problem is present only when the X coodinates of the points are near each other

José Luis García Pallero <jgpallero>

 

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Attached Files
file #35128:  test_errorbar.pdf added by jgpallero (3KiB - application/text-plain:formatted)

 

Depends on the following items: None found

Items that depend on this one: None found

 

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    Follow 4 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2015-10-09 rik5 StatusNone => Postponed
    2015-10-09 rik5 CategoryPlotting => Plotting with OpenGL
        SummaryBug in errorbar() when X coordinates are near each other => OpenGL use of single causing problems in errorbar
    2015-10-09 jgpallero Attached File- => Added test_errorbar.pdf, #35128

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