# RE: FLAIR projections and statistical error

From: Santana, Mario <msantana_at_SLAC.Stanford.EDU>
Date: Tue, 15 Feb 2011 14:34:49 -0800

Roger,

Let's take as an example a 2D plot. Usually you will want to plot a
3D matrix generated by USRBIN.
But the plot can only be made in 2D, so you need to choose what kind of
view you want (e.g. elevation, plain, cross section ~ X, Y, Z depending on
your reference frame). If you project the matrix on the y-z plane (X axis),
you will be plotting a {y, z} mesh in which each point {y_j, z_k} is the
average value of all the layers with the same {y_j, z_k} but different x_i
(x_1, x_2...). If you specify limits for your x axis, then FLAIR will only take
into account all the layers between your specified x range. The associated
error, for any {y_j, z_k} bin is obtained in FLAIR by calculating the
relative error of the sum of bins and dividing by the square root of the
numberof terms. In FLAIR you can actually select the 'error' box to plot the
associated relative errors. If you do so, remember to set the normalization
factor to 1 and to use a scale ranging from 0 (or close) to 100.

Anyway, in most practical cases, if your plot looks smooth (isolines are
well defined, no big traces, nor 'random' fluctuations in neighboring values)
most likely your statistical error will be acceptable. Of course, this
depends on the scale range that you use, so use good judgment.

Mario

-----Original Message-----
From: owner-fluka-discuss_at_mi.infn.it [mailto:owner-fluka-discuss_at_mi.infn.it] On Behalf Of Roger Haelg
Sent: Tuesday, February 15, 2011 6:01 AM
To: fluka-discuss_at_fluka.org
Subject: FLAIR projections and statistical error

Dear FLUKA and FLAIR experts

Could anyone explain to me what the "projection& limits" for data plots
(1d and 2d) in FLAIR exactly do with the data for plotting? The manual
does not explain this.

And what happens to the statistical error in this case? The manual says:
"WARNING errors will be underestimated, since it treats all bin values
as uncorrelated."
How can I estimate the error when using this projections and limits for
several bins? Are there different cases to be differentiated?

In the FLUKA course materials there is a table listing the statistical
errors and the usefulness of the results. Is this always related to the
statistical errors of the individual bin or is there a way to estimate
the error using projections and averaging?

Thank you very much for your help!

Regards,

Roger Haelg
Received on Wed Feb 16 2011 - 09:25:41 CET

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