Hi HCP!
As I was going through the scripts for generating HCP 820-subject PTN
release, there is a step in script "subproc_DO_2_groupPCA.m" that seems
quite confusing to me. The part of code is pasted as follows:
*BO=ciftiopen(f{r(1)},WBC); grot=demean(double(BO.cdata)'); clear BO.cdata;*
*[uu,ss,vv]=ss_svds(grot,30); vv(abs(vv)<2.3*std(vv(:)))=0;
stddevs=max(std(grot-uu*ss*vv'),0.001);
grot=grot./repmat(stddevs,size(grot,1),1); % var-norm*
*W=demean(grot); clear grot;*
This is done to every individual run and it's supposed to temporally demean
and variance normalize the data. Why is this way (marked in bold) used to
compute the stddevs? And how is this number 30 in the ss_svds chosen? It
seems to be fixed and not relative with the dimension of ICA.
Thanks for any clarification!
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