[Eeglablist] AMICA lrate gets stuck

[Kevin Tan]

Hi Jason,

Thanks so much for the detailed response, really helps clarify what drives
the lrate changes between the two implementations.

However, for the same dataset processed the same way, AMICA yields higher
wchange at last iteration (0.0000464763) versus extended Infomax
(0.000000).

What are some reasons for this discrepancy, and what can I do improve it?
Or is weight change between the two implementations not comparable? The
entire AMICA log is linked in original post if that helps.

Thanks again,
Kevin

--
Kevin Alastair M. Tan
Lab Manager/Research Assistant
Department of Psychology & Center for the Neural Basis of Cognition
Carnegie Mellon University

Baker Hall 434
<https://www.google.com/maps/place/40%C2%B026%2729.5%22N+79%C2%B056%2744.0%22W/@40.4414869,-79.9455701,61m/data=!3m1!1e3!4m2!3m1!1s0x0:0x0>
 | kevintan at cmu.edu | tarrlab.org/kevintan
<http://tarrlabwiki.cnbc.cmu.edu/index.php/KevinTan>

On Mon, Aug 17, 2015 at 7:06 PM, Jason Palmer <japalmer29 at gmail.com> wrote:

> Hi Kevin,
>
>
>
> The Amica lrate is not supposed to decrease. The algorithm is a more
> typical gradient descent / Newton optimization algorithm, as opposed to the
> Infomax implementation in runica.m, which uses a type of simulated
> annealing, deciding whether to reduce the learning rate based on the angle
> between recent update directions. The idea there is that this angle will be
> small when the algorithm is near an optimum, as though it is “heading right
> for it”, so the lrate gets reduced if the algorithm is moving “erratically”
> with a large angle between consecutive directions, and doesn’t get reduced
> if the estimate is “moving smoothly”. In practice, this annealing method
> usually ends up in fact reducing the learning rate continuously until it
> reaches the preset minimum, which usually happens at around 500 iterations
> (500 reductions). I.e. the angle is never actually small, so the stopping
> condition is essentially a maximum number of iterations, with the updates
> being of smaller and smaller magnitude due to the lrate decreasing.
>
>
>
> Amica only reduces the lrate if the likelihood decreases. In theory, with
> a reasonable optimum, an optimization algorithm should be able to converge
> without reducing the learning rate. The convergence is measured by the
> weight change (the nd in the amica output) independently of the lrate. That
> is, the weight change should theoretically decrease to zero with a constant
> (sufficiently small) lrate—the higher the better since higher lrate means
> faster convergence. A potential issue with the runica Infomax is early
> convergence if you are starting far from the optimum. Fortunately the
> optimum is usually not far from the “sphering” starting point, so 500
> iterations is usually enough to converge (even with decreasing lrate).
>
>
>
> So in Amica, the convergence is judged by the “nd”, not the lrate. The
> lrate should be ideally be 0.5 or 1.0, and the LL should be increasing, and
> the nd should be decreasing to zero.
>
>
>
> Hope that is helpful.
>
>
>
> Best,
>
> Jason
>
>
>
>
>
> *From:* Kevin Tan [mailto:kevintan at cmu.edu]
> *Sent:* Monday, August 17, 2015 2:31 PM
> *To:* jason at sccn.ucsd.edu; EEGLAB List
> *Subject:* AMICA lrate gets stuck
>
>
>
> Hi Dr. Palmer & EEGLAB list,
>
>
>
> I'm trying out AMICA for artifact rejection and DIPFIT. In my tests, the
> lrate consistently gets stuck at 0.5, stopping only due to max iteration
> limit. This does not happen with extended Infomax.
>
>
>
> This happens whether I use the cluster (128 threads) or a normal PC (4
> threads). I run AMICA 'locally' as it's called within a matlab script
> already run via PBS, not sure if that makes a difference.
>
>
>
> Here's the AMICA test stream:
>
> - PREP pipeline
>
> - Remove PREP-interpolated channels
>
> - Remove 1 additional channel for rank consistency
>
> - 1hz FIR hi-pass
>
> - Epoch -500 to 1000ms no baseline correction
>
> - Epoch rejection
>
> - AMICA (using EEG(:,:) -- is it ok to concatenate epochs like this?)
>
>
>
> Here's the output log (using the cluster):
>
> https://cmu.box.com/s/t7j3shmwjj1wj8to80au8mdm6b5676rh
>
>
>
> Many thanks,
>
> Kevin
>
> --
>
> Kevin Alastair M. Tan
>
> Lab Manager/Research Assistant
>
> Department of Psychology & Center for the Neural Basis of Cognition
>
> Carnegie Mellon University
>
>
>
> Baker Hall 434
> <https://www.google.com/maps/place/40%C2%B026%2729.5%22N+79%C2%B056%2744.0%22W/@40.4414869,-79.9455701,61m/data=!3m1!1e3!4m2!3m1!1s0x0:0x0>
>  | kevintan at cmu.edu | tarrlab.org/kevintan
> <http://tarrlabwiki.cnbc.cmu.edu/index.php/KevinTan>
>
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