Re: Connecting error bars with polygon?

From: Georg Troska <georg.troska_at_uni-dortmund.de>
Date: Mon, 14 Nov 2011 18:24:42 +0100

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

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> 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 Mon Nov 14 2011 - 18:24:55 CET