My default interpretation of errors is always relative to the value because that is how they are reported (100+10-20 not 100+110-80).
(got your 2nd email while writing this) Would you find this clearer? Maybe xerr and yerr should be split up xerr/yerr: [ scalar | N, Nx1, or 2xN array-like ] If a scalar number, len(N) array-like object, or an Nx1 array-like object, errorbars are drawn x/y +/- value. If a sequence of shape 2xN, errorbars are drawn at x/y - row1 and x/y + row2 Tom On Sat, Feb 9, 2013 at 12:49 PM, Markus Haider <markus.hai...@uibk.ac.at> wrote: > Hi Tom, > > Thank you very much for your answer. Indeed this solves my problem. However, > I was wondering if the documentation on this is correct. > At > http://matplotlib.org/api/axes_api.html?highlight=errorbar#matplotlib.axes.Axes.errorbar > it says: > > xerr/yerr: [ scalar | N, Nx1, or 2xN array-like ] > If a scalar number, len(N) array-like object, or an Nx1 array-like object, > errorbars are drawn +/- value. > If a sequence of shape 2xN, errorbars are drawn at -row1 and +row2 > > This sounds to me that for a 2xN argument it should be drawn from the actual > supplied value, or would you interpret this differently? > > Thanks, > Markus > > Am 2013-02-08 22:02, schrieb Thomas Caswell: > >> The bar is drawn from `y - yerr_low` to `y + yerr_upp` >> >> ax.errorbar(x + .5,y,yerr=[[y - yerr_low],[yerr_upp - >> y]],fmt='s',markersize=4) >> >> will get you what you want. >> >> Tom >> >> On Fri, Feb 8, 2013 at 8:41 PM, Markus Haider <markus.hai...@uibk.ac.at> >> wrote: >>> >>> Hi, >>> >>> I think I have a problem with errorbars in a log plot. The problem is >>> reproducible through the enclosed errorbar_log.py file. As you can see I >>> plot a point with y = 10**(-5) and I want the errorbars drawn from >>> 10**(-5.5) to 10**(-4.5) which should be symmetric in this plot but >>> isn't. >>> >>> Here is the content of my errorbar_log.py file: >>> >>> #!/usr/bin/python >>> import numpy as np >>> import matplotlib.pyplot as plt >>> >>> fig = plt.figure() >>> ax = fig.add_subplot(111) >>> x = 0.0 >>> y = 10**(-5.0) >>> yerr_low = 10**(-5.5) >>> yerr_upp = 10**(-4.5) >>> ax.errorbar(x,y,yerr=[[yerr_low],[yerr_upp]],fmt='o',markersize=4) >>> ax.set_xlim(-1.0,1.0) >>> ax.set_ylim(1E-6,1E-3) >>> ax.set_yscale('log') >>> plt.savefig('errorbar.png') >>> >>> --------------------------------------------- >>> >>> 10**(-5.5) = 3.162277660168379e-06 >>> and 10**(-4.5) = 3.1622776601683795e-05 >>> >>> but you can see that the lower boundary is not at the calculated value. >>> <http://matplotlib.1069221.n5.nabble.com/file/n40412/errorbar.png> >>> >>> >>> Do I misunderstand the behaviour of the errorbar function or is this a >>> bug? >>> >>> Cheers, >>> Markus >>> >>> >>> >>> -- >>> View this message in context: >>> http://matplotlib.1069221.n5.nabble.com/Errorbar-problem-tp40412.html >>> Sent from the matplotlib - devel mailing list archive at Nabble.com. >>> >>> >>> ------------------------------------------------------------------------------ >>> Free Next-Gen Firewall Hardware Offer >>> Buy your Sophos next-gen firewall before the end March 2013 >>> and get the hardware for free! Learn more. >>> http://p.sf.net/sfu/sophos-d2d-feb >>> _______________________________________________ >>> Matplotlib-devel mailing list >>> Matplotlib-devel@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel >> >> >> >> -- >> Thomas Caswell >> tcasw...@gmail.com >> > -- Thomas Caswell tcasw...@gmail.com ------------------------------------------------------------------------------ Free Next-Gen Firewall Hardware Offer Buy your Sophos next-gen firewall before the end March 2013 and get the hardware for free! Learn more. http://p.sf.net/sfu/sophos-d2d-feb _______________________________________________ Matplotlib-devel mailing list Matplotlib-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-devel
