Dear Matthew
thank for you answer. Unfortunately, I can only calculate the result with upgraded FSL on one of the two machines (Ubuntu 12.04) since I do not have administrator privileges for the other one. With FSL 5.01 I get the 'rounding up' result, i.e.
echo 11 > thresh_zstat1.vol
zstat1: DLH=0.0883917 VOLUME=11 RESELS=56.0059
/usr/share/fsl/5.0/bin/ptoz 0.05 -g 1
2.000748
I am still a bit reluctant to take this result of this calculation as is. I rather prefer to fully understand the matter and like to figure out what would be the correct result if this step of the analysis were done by hand.
Reading the comments on this mailing list regarding the calculation of the resel count for the correction indicates that the correct answer for the -g option should be 0.196407878 (i.e. #resels= VOLUME/RESELS -> 11/56.0059=0.196407878). For this value ptoz returns me 0. The interpretation of this result would be that the volume does not fill out an entire resel and therefore no correction is necessary.
This is however not what FEAT 6.0 does. Here it rounds up (I interpret this as 'even if this volume of interest is not equivalent to a full resel, one would correct for at least 1 resel).
So maybe I went wrong in the calculation of the number of resels, or there is an implicit rounding rule (which I do not know off), or the software does an incorrect calculation for this extreme case (at least on Ubuntu 12.04).
Hence in order to solve this discrepancy, I should probably rephrase my question (and apologize if I should have started a new thread) and ask: Given the values above, which value is the correct one to use for the -g option of ptoz?
Thanks a lot!
Stephan
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