Re: Connecting error bars with polygon?

I still have problems how to correctly calculate an error band

The errors band are simply drawn using the errors. It is simply an other way to draw the errors. I guess you should know what the errors of your graphs should be … ?

On Nov 14, 2011, at 6:24 PM, Georg Troska wrote:

Yes great, this works...

unfortunately I still have problems how to correctly calculate an error band. I have added an example with some points and a linear "pol1" fit. I calculated the gaussian error for each point (presuming the points to be measured independent, which they are not) and plotted it as error band.

I would expect, that the error-band overlaps with the points in 2/3 of all cases. What I see is much less.

So my questions are:

1. Is there a much more simple way how to draw an error-band (maybe a draw-option for the TF1?)
2. Does the GetParError() Method really provide the correct error for each value, calculated with gaussian error propagation?
3. I have heard somewhere that the error values need to be scaled with *= sqrt(chi2/ndf-1) - Do they, or don't they?
4. Where is the mistake in my attached example?

Thanks a lot - and sorry for my confusion

Georg

<fittest2.C>

Am 10.11.2011 um 14:55 schrieb Olivier Couet:

See:

http://root.cern.ch/root/html/TGraphPainter.html#GP03

On Nov 10, 2011, at 2:50 PM, Mohammed Zakaria wrote:

Hi,

Try something like:
Try using class TGraphErrors (name it for example f1), there you will find the option:
f1 -> Draw("E3 same");

Best,

Mohammed Zakaria

On Thu, Nov 10, 2011 at 7:42 AM, Georg Troska
<georg.troska_at_uni-dortmund.de<mailto:georg.troska_at_uni-dortmund.de>> wrote:
Hi,

I would like to plot the significance-area of a fit function. But I do not want to use error bars, but something like a colored region - A polygon through the ends of invisible error-bars would be fine. I think it is possible to make an exclusion plot (see example in manual) but in this case the exclusion width needs to be constant.

simple example could be:

function y=x [0,10]
and the error is e(y) = 0.1*x

Hope its clear, what I want to say? Hard to explain... hope someone has a hint

Thanks Georg Received on Tue Nov 15 2011 - 10:24:52 CET