Per the name "zcorr", the correlation values have been z-transformed (fisher's small z transform). I am somewhat confused as to why some elements in the diagonal are not infinite. The "true" value of applying this transform would be infinite on the entire diagonal, as arctanh(1) is infinite. I am guessing this result was generated in matlab, as wb_command actually prevents infinities when using the z transform, putting a cap on the correlation (when not using z-transform, it shows correlations of 1 as expected).
Whatever analysis you do with correlation matrices like this should ignore the diagonal anyway, since it is correlation to itself. Tim On Mon, May 15, 2017 at 3:57 AM, Sang-Yun Oh <[email protected]> wrote: > I downloaded group average functional correlation file: HCP_S900_820_rfMRI_ > MSMAll_groupPCA_d4500ROW_zcorr.dconn.nii > > Some diagonal elements of the square matrix (91282x91282) are infinite > (Please see below). > > I want to use this matrix in ananalysis; however, I am not sure how to > understand or deal with infinite diagonal values. > > I appreciate any insight > > Thanks, > Sang > > ====================== > > In [1]: import nibabel > > In [2]: asdf = nibabel.load('HCP_S900_820_rfMRI_MSMAll_groupPCA_ > d4500ROW_zcorr.dconn.nii') > > In [3]: img = asdf.get_data() > > In [4]: img.shape > Out[4]: (1, 1, 1, 1, 91282, 91282) > > In [5]: S = img[0,0,0,0,:,:] > > In [6]: S > Out[6]: > memmap([[ 8.66434002e+00, 1.96847185e-01, 1.66294336e-01, ..., > 1.01449557e-01, 7.45474100e-02, 1.15624115e-01], > [ 1.96847185e-01, inf, 3.36383432e-01, ..., > -5.70017472e-03, -5.49946353e-02, 3.72834280e-02], > [ 1.66294336e-01, 3.36383432e-01, inf, ..., > -4.45242636e-02, -6.07097335e-02, -1.51601573e-02], > ..., > [ 1.01449557e-01, -5.70017472e-03, -4.45242636e-02, ..., > inf, 1.91883039e+00, 9.20160294e-01], > [ 7.45474100e-02, -5.49946353e-02, -6.07097335e-02, ..., > 1.91883111e+00, 8.31776619e+00, 8.82132888e-01], > [ 1.15624115e-01, 3.72833721e-02, -1.51601573e-02, ..., > 9.20160294e-01, 8.82132888e-01, 8.66434002e+00]], > dtype=float32) > > In [7]: S.diagonal() > Out[7]: > memmap([ 8.66434002, inf, inf, ..., inf, > 8.31776619, 8.66434002], dtype=float32) > > > _______________________________________________ > HCP-Users mailing list > [email protected] > http://lists.humanconnectome.org/mailman/listinfo/hcp-users > _______________________________________________ HCP-Users mailing list [email protected] http://lists.humanconnectome.org/mailman/listinfo/hcp-users
