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Re: Proposal for Matlab style errorbars

From: Ben Abbott
Subject: Re: Proposal for Matlab style errorbars
Date: Fri, 30 Apr 2010 07:58:14 -0400

On Apr 29, 2010, at 8:49 PM, Ben Abbott wrote:

> On Apr 29, 2010, at 3:37 PM, David Bateman wrote:
>> Ben Abbott wrote:
>>> I've modified __errplot__.m to produce Matlab style errorbars, and would 
>>> like some feedback before pushing.
>>> I'm not sure how the box style error bars (#) are supposed to look. For my 
>>> setup they look identical to the normal ones (i.e. "#~>" looks like "~>"). 
>>> Rather than duplicate the same "look", I made the box styles look like 
>>> "boxes".
>>> I haven't pushed this yet, but did add some demos to errorbar.m. I 
>>> recommend pulling that change to make testing/demoing this changeset easier.
>>> Of course, as an added bonus, this implementation works with the fltk 
>>> backend.
>>> Ben
>>> p.s. I hope no one minds that I cc'd everyone involved in the discussion on 
>>> the bug tracker. 
>> As far as I can see the changes to __errplot__ itself are cosmetic.. The big 
>> change is in the updata_data subfunction and with the little testing i've 
>> done it seems ok. I have two points however. If we make this change to would 
>> be a good idea to try and pick the same parameters using in the errorbar 
>> lines in the matlab version of this. I don't have matlab. In particular is 
>> the value of  dx,  etc the same as used in matlab? It would also make sense 
>> to remove the ldata, udata, xldata and xudata from the line objects of 
>> Octave, and from __go_draw_axes__ as they will no longer be used after this 
>> patch. This values will only be in the hggroup itself
>> Cheers
>> David
> I've verified the width of the error-bar by ...
>       xmax = 100;
>       figure(1)
>       clf
>       x = [0, xmax];
>       y = [0, 0];
>       dx = diff(x)/100;
>       err = [1 1]*dx;
>       errorbar (x, y, err, '-sb')
>       axis equal
>       axis ([-2 2 -2 2]*dx)
> Independent of the value for xmax, the resulting errorbar fits into a perfect 
> square. I think this confirms that dx = (max(x)-min(x))/100;
> This matches what I saw in the figured linked to below.
>       http://www.mathworks.se/matlabcentral/fx_files/22826/4/errorbar_tick.gif
> I'll remove the FIXME comment regarding the errorbar width.
> It occurred to me today that semilogxerr, semilogyerr, and  loglogerr each 
> call __errplot__ as well. I'll modify dx so that it works correctly with 
> axes.scale=="log".
> Once I've pushed the change to __errplot__, I'll take care of 
> __go_draw_axes__.m and graphics.h.in.
> Ben

I've pushed the change below (which supports semilogxerr, semilogyerr, and 


I plan to work on __go_draw_axes__.m and graphics.h.in this weekend.


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