Hi Joseph,
thanks for the interesting question!
(1) "Can I give errors as absolute min/max values instead of differences"?
-> Yes, especially if you have table input: you can use 'y error
expr=<expression>' where <expression> is some math expression which may
depend on \thisrow{<colname>} (the syntax is actually the same as for y
expr=<expression>).
(2) "Can I have asymmetric error bars?"
-> Pgfplots currently expects symmetric error values (there are pending
feature requests to add asymmetric error bars).
At the time of this writing, a good work-around is to use the same plot
twice: once for upper and once for lower error values. In addition, one
of them should have "forget plot" to avoid a legend entry.
A complete working example with your data could be
\documentclass{article}
\usepackage{pgfplots}
\begin{document}
\begin{tikzpicture}
\begin{axis}
\addplot+[forget plot,error bars/.cd,y dir=plus,y explicit]
table[x=x,y=y,y error expr=\thisrow{y_max}-\thisrow{y}] {
x y y_min y_max
1 0.01 -0.01 0.02
2 0.03 0.00 0.035
3 -0.05 -0.06 -0.04
4 0.06 0.05 0.07
};
\addplot+[error bars/.cd,y dir=minus,y explicit]
table[x=x,y=y,y error expr=\thisrow{y}-\thisrow{y_min}] {
x y y_min y_max
1 0.01 -0.01 0.02
2 0.03 0.00 0.035
3 -0.05 -0.06 -0.04
4 0.06 0.05 0.07
};
\end{axis}
\end{tikzpicture}
\end{document}
Clearly, you will only provide the data once (either from file or using
\pgfplotstableread) -- but you get the idea.
Your approach appears to have a similar effect: the idea with two data
sets is the same as my answer for (2). The centered set will work as
well from what I understand.
I hope you enjoyed christmas! My best wishes for the new year!
Best regards
Christian
Am 23.12.2011 23:19, schrieb Joseph Wright:
> On 23/12/2011 20:52, Joseph Wright wrote:
>> Hello Christian,
>>
>> A quick pgfplots question. I have some data where I have ranges for the
>> y value, so something like
>>
>> x y y_min y_max
>> 1 0.01 -0.01 0.02
>> 2 0.03 0.00 0.035
>> 3 -0.05 -0.06 -0.04
>> 4 0.06 0.05 0.07
>>
>> This is easy enough to put in using an external table, but I can't find
>> a reference in the manual to either (1) giving errors as absolute
>> max/min values rather than as shits and (2) different errors on the plus
>> and minus side of a value. Am I correct in thinking that at present this
>> can't be done using pgfplots?
>>
>> Regards,
>>
>> Joseph
> Hello Christian
>
> Ah, I've worked it out: do two columns of y values, the real set and a
> centred set, and use the later for the error bars.
>
> Joseph
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