[Eeglablist] Saving data set changes rank

[Hiebel, Hannah (hannah.hiebel@uni-graz.at)]

Hi John,


I encountered a similar problem a while ago and realized that depending on a combination of different settings in the memory options (option_savetwofiles, option_single), the precision of the data potentially changes when saving a dataset (single vs. double).

The precision, in turn, appears to affect the result returned by rank(EEG.data). For double precision, the rank corresponded to the number of channels; when converting the same data to single precision, the rank changed to a comparatively low value (similar to what you report).


You could check the precision before and after saving the dataset; maybe your problem is related to this aspect?


Best,

Hannah


________________________________
Von: eeglablist <eeglablist-bounces at sccn.ucsd.edu> im Auftrag von Johnson, John T. <john.johnson at gatech.edu>
Gesendet: Mittwoch, 16. Mai 2018 20:24
An: eeglablist at sccn.ucsd.edu
Betreff: [Eeglablist] Saving data set changes rank

When I load a data set, the rank of the data is 58, the same as the number of channels.
Making no changes and saving the data set with another name, the rank changes to 1.
I like saving data at various check points while preprocessing, and this change in rank can affect specifying rank for the pca option to ica, or pcakeep to AMICA.
Any ideas?

>> EEG = pop_loadset('filename','pre_p36_nv_to.set','filepath','Processed/');
pop_loadset(): loading file Processed/pre_p36_nv_to.set ...
Reading float file 'Processed/pre_p36_nv_to.fdt'...
>> rank(EEG.data)

ans =

    58

>> EEG = pop_saveset( EEG, 'filename', 'rankdef.set' );
Saving dataset...
>> rank(EEG.data)

ans =

     1

>> rank(EEG.data')

ans =

     1


Thanks,
John

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