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Re: Request for information on ICA-Maximum likelihood approach
Brian Gygi wrote:
Doesn't that kind of negate the whole purpose of ICA?
Not quite. PCA enforces the rule that components must contain the
maximal amount of variance not accounted for by previous components.
Where as ICA returns (depending on the ICA algorithm) maximally
temporally (or spatially) independent sources. There is no restriction
on how much variance (usually) the components must account for only that
they are independent.
It's supposed to
find the dimensions that PCA might miss. But if you do a PCA first, all
you will get out are subsets of the dimensions the PCA finds in the
There are also good reasons why you should run PCA (for big data sets)
where the number of channels might approach (or be larger than) the
square root of the number of sample points. This has the effect of
having a "better" number of data points for the ICA weight matrix:
Although again this might depend on the ICA algorithm being used.
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