hi Eric, then I misunderstood what the code does.... I thought it was transforming the data. In any case, my second figure in my previous post is wrong because the code should read: plt.errorbar(cE,corrE*fluxes, yerr=corrE*unc_fluxes) instead of plt.errorbar(cE,corrE*fluxes, yerr=unc_fluxes)
and indeed this seems to behave correctly, so I guess I got completely confused while trying to understand what was happening. I will check out your patch and start from the beginning. thanks a lot and sorry, Johann Eric Firing wrote: > Cohen-Tanugi Johann wrote: >> ok, maybe it is in scale.py :) >> And what I see there confirms my initial fears : the log scale >> transform applies a log to the argument, which is incorrect for an >> error..... So first of all, another transform needs to be created so >> that erry is transformed into erry/y/log(base) where base was 10 in >> my example. > > Johann, > > I don't understand your objection here. It seems to me that an > errorbar should always be in the same units, and on the same scale, > as the point to which it applies. Therefore when switching from > linear to log scales, one simply plots the same data and error ranges > on a log scale instead of a linear scale. This is what mpl does. If > what you want is for the error to be proportional to the value of the > point, then you need to specify the error bounds so that they have > that property. For estimation of a power spectrum, for example, this > is often the case; the error bars are some fraction (depending on the > equivalent number of degrees of freedom) of the spectral level at each > frequency, so on a log plot they will have equal length. It is not > the job of the errorbar function to figure that out, however. > > If I am misunderstanding, then please provide a very simple concrete > example that will make your point clear. > >> >> past midnight here.... I will see tomorrow if I find time to try out >> a patch (not the easiest entry point for starting developer's >> activities in MPL I am afraid....) > > I have just committed a change (trunk r7023) that allows non-positive > numbers to be clipped to a small positive value. To illustrate its > use with an errorbar, I added the example provided by Matthias to > examples/pylab_examples/log_demo.py, as a 4th subplot. > > Eric >> >> Johann ------------------------------------------------------------------------------ _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
