New low-level routines for mtmconvol and mtmfft implemented

Tue Jul 27 17:45:34 CEST 2010

Hi Vladimir,

Well, it wasn't that final yet, I actually meant to sent the e-mail to
dev-mailing list ;). I had a short discussion with Jan-Mathijs on it,
but since it wasn't going live yet it didn't matter that much. The
tapsmofrq being variable I realized doesn't necessarily mean different
number of tapers, so I will implement that in the new-implementation
tomorrow (tiny changes). However, implementing variable number of tapers
requires some more thorough design decisions for the new low-level
functions (especially in terms of consistent data representation
throughout all low-level functions). Perhaps we should discuss this in
more detail in the dev-mailing list? I'm sure Jan-Mathijs will join,
Robert is on vacation at the moment.

But thanks for your reply!

Best,
Roemer

On 7/27/2010 4:58 PM, Vladimir Litvak wrote:
> Dear Roemer,
>
> Why did you decide to drop the support for variable number of tapers
> in mtmconvol? That was actually quite a handy feature that I'm using
> to get TFs with more or less uniform smoothness across frequency. I
> don't know how many other people are using it but if there are many
> perhaps we can campaign for retaining it in the new implementation ;-)
>
> Best,
>
> Vladimir
>
> On Tue, Jul 27, 2010 at 3:48 PM, Roemer van der Meij
> <r.vandermeij at donders.ru.nl <mailto:r.vandermeij at donders.ru.nl>> wrote:
>
>     Hi everybody,
>
>     I just finished fully implementing the new low-level frequency
>     analysis routines for cfg.method = mtmconvol and mtmfft. They are
>     not yet used by default, and I would appreciate if it can be
>     tested more before optimizing computation speeds (should be
>     relatively equal now, but many optimizations possible).
>
>     The new routines can be used by adding a third input argument to
>     your ft_freqanalysis calls, as:
>     New implementation:
>     freq = ft_freqanalysis(cfg,data,1)
>     Old implementation (default):
>     freq = ft_freqanalysis(cfg,data,0)
>
>     *Things that are different:*
>     - all mtmconvol output is now phase-shifted such that an angle of
>     0 of any fourier-coefficient /always /means a peak of an
>     oscillation in the data, and an angle of pi will /always/ mean the
>     trough of an oscillation (wavelet wise angle = 0 is implemented as
>     cosine at peak, and sine in up-going flank)
>     - all mtmfft output is now phase-shifted such that any angle from
>     any fourier-coefficient is from the perspective of the oscillation
>     in the data being at its peak at time = 0
>     - mtmconvol now uses an accurate frequency vector for building its
>     wavelets (determined by fsample and nsample, with cfg.foi as
>     starting point), instead of an /uncorrected/ cfg.foi (mtmfft
>     already used an accurate one) (note: this causes slight
>     differences between the old and new implementation)
>     - mtmfft can now take a cfg.foi input-vector as well, instead of
>     the usual cfg.foilim (backwards compatible)
>     - because of the above, nearly /all/ fourier-output is different,
>     but e.g. phase differences between coefficients should be the same
>     - we decided to drop the support for variable number of tapers in
>     mtmconvol, cfg.tapsmofrq can only be a scalar now (warning is
>     given, and first element of vector is selected)
>      - in the new format, many things can be upgraded/implemented etc.
>     in the future
>
>
>     As freqanalysis is a rather fundamental pilar of FieldTrip, I
>     would really appreciate if some of you can do some testing based
>     on the above differences and anything else you can think of.
>     Different types of data, different approaches, etc. to see if both
>     implementations give comparable results and such (do note raw
>     fourier-coefficients will almost always be different). It could be
>     I missed some fields from the old functions that I diligently
>     checked, or made some errors that did not affect my current
>     testing environment.
>     I can be reached at the e-mail address below, via the
>     mailing-list, or via bug-reports. Thanks in advance.
>
>     All the best!
>
>     Roemer
>
>
>     PS: the changes will be on the ft-server tonight, but are of
>     course already in the svn-version
>
>     --
>     Roemer van der Meij MSc
>     PhD student
>     Donders Institute for Brain, Cognition and Behaviour
>     Centre for Cognition
>     P.O. Box 9104
>     6500 HE Nijmegen
>     The Netherlands
>     Tel: +31(0)24 3655932
>     E-mail:r.vandermeij at donders.ru.nl  <mailto:r.vandermeij at donders.ru.nl>
>
>     ----------------------------------
>
>     The aim of this list is to facilitate the discussion between users
>     of the FieldTrip toolbox, to share experiences and to discuss new
>     ideas for MEG and EEG analysis.
>
>     http://listserv.surfnet.nl/archives/fieldtrip.html
>
>     http://www.ru.nl/fcdonders/fieldtrip/
>
>
> ----------------------------------
>
> The aim of this list is to facilitate the discussion between users of
> the FieldTrip toolbox, to share experiences and to discuss new ideas
> for MEG and EEG analysis.
>
> http://listserv.surfnet.nl/archives/fieldtrip.html
>
> http://www.ru.nl/fcdonders/fieldtrip/
>

--
Roemer van der Meij MSc
PhD student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognition
P.O. Box 9104
6500 HE Nijmegen
The Netherlands
Tel: +31(0)24 3655932
E-mail: r.vandermeij at donders.ru.nl

----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.
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