Q:

Asymmetric Error Bars in MatPlotLib

I have a loglog plot and would like to plot positive error bar for one of the 6 data points. The rest can have positive & negative. How do I work this out? 
Generally this is how I have plotted error bars: 
plt.loglog(vsini_rand, vsini_rand_lit, 'bo', label='Randich+1996')
plt.errorbar(vsini_rand, vsini_rand_lit, xerr = sig_rand, color = 'gray', fmt='.', zorder=1)
plt.loglog(x,y,'r-', zorder=3, label='1:1')

A:

Reading the documentation of plt.errorbar, if you want to plot asymmetric errorbars, you would have to use the argument of xerr as a sequence of shape 2xN. If you do so, errorbars are drawn at -row1 and +row2 relative to the data. If you want to plot a positive error bar for only one point, you should define to zero the lower limit. I mean, if your data is:
[x1, x2, ... , xn]

you have to give the sequence:
[x0-,x0+,x1-,x1+, ... , xn-,xn+] 

as the argument of xerr.
Hope it helps.

