[FieldTrip] File Size depends on No. of Trials?

[Claudio Georgii]

Hi Christine,

In addition you could change the precision from double to single (which
reduces the working memory needed by a half). As far as i know, double
precision is not needed here and single should do fine, but please correct
me if I am wrong.

Claudio

2016-11-30 10:31 GMT+01:00 Julian Keil <julian.keil at gmail.com>:

> Hi Christine,
>
> take a look into the cfg.previous of ERDERS. Fieldtrip stores information
> on previous data analysis steps there. Maybe the trial information is
> hidden somewhere in there.
> The MatLab command rmfield can then be used to remove some unwanted fields
> from a structure. But please beware! There is a good reason for the
> thorough bookkeeping in Fieldtrip (which has saved me quite often).
> Good luck,
>
> Julian
>
> On Wed, Nov 30, 2016 at 10:25 AM, Blume Christine <
> christine.blume at sbg.ac.at> wrote:
>
>> Dear Community,
>>
>>
>>
>> I have an issue with data size. I am processing high-density EEG data
>> from a sleep study. Following preprocessing I perform time-frequency
>> transformations and a baseline correction using the following code:
>>
>>
>>
>>         cfg = [];
>>
>>         cfg.method = 'wavelet';
>>
>>         cfg.output = 'pow';
>>
>>         cfg.keeptrials = 'no';
>>
>>         cfg.width = 3; %
>>
>>         cfg.foi = 1:1:16; %
>>
>>         cfg.toi = -0.7:0.2:0.9;
>>
>>         freqanalysis_FV = ft_freqanalysis(cfg, data_FV);
>>
>>
>>
>>         cfg = [];
>>
>>         cfg.baseline = [-0.6, 0];
>>
>>         cfg.baselinetype = 'relchange';
>>
>>         ERDERS_FV = ft_freqbaseline(cfg, freqanalysis_FV)
>>
>>
>>
>> As you can see, I do *not* keep the trials. Still, the size of ERDERS
>> seems to depend on the size of data_FV. Why is that the case? Also,
>> changing cfg.foi does not change the file size – why? The problem is that
>> this way the data can hardly be handled as it takes up so much RAM. Please
>> note that I do clear everything from the workspace I do not need, that
>> should not be the issue.
>>
>>
>>
>> Thanks a lot for your thoughts.
>>
>>
>>
>> Best,
>>
>> Christine
>>
>>
>>
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>
>
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-- 
Claudio Georgii, MSc.
Phd student
University of Salzburg - Department of Psychology
Eating Behavior Laboratory
Hellbrunnerstraße 34
5020 Salzburg - Austria

Phone: 0043- (0)662 8044 5164
E-Mail: claudio.georgii at sbg.ac.at
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