oh...do you mean he is not gonna reply the questions in this Email list any longer?
Xuelin
****************************************
Xuelin Cui
Department of Electrical Engineering
University of Hawaii-Manoa
Honolulu HI 96822
Tel: 1-808-349-0983
Email: [log in to unmask]
****************************************
----- Original Message -----
From: Tim Behrens <[log in to unmask]>
Date: Monday, March 12, 2007 12:08 pm
Subject: Re: [FSL] some theoretical questions on MELODIC
To: [log in to unmask]
> No - I'm afraid not. He is away.
>
> Tim
>
> On 12 Mar 2007, at 22:04, Xuelin Cui wrote:
>
> > Yes, I am reading that, and I am stuck on that. That's why I want
>
> > to ask Christian, coz he wrote the report.
> >
> > Do you know when he will be back on Email again?
> >
> > Thanks
> >
> > Xuelin
> >
> > ****************************************
> > Xuelin Cui
> > Department of Electrical Engineering
> > University of Hawaii-Manoa
> > Honolulu HI 96822
> >
> > Tel: 1-808-349-0983
> > Email: [log in to unmask]
> > ****************************************
> >
> > ----- Original Message -----
> > From: Tim Behrens <[log in to unmask]>
> > Date: Monday, March 12, 2007 11:43 am
> > Subject: Re: [FSL] some theoretical questions on MELODIC
> > To: [log in to unmask]
> >
> >> Hi -
> >> Christian is away at the moment I'm afraid. He is off email, but
> >> did
> >> you see that steve answered your questions as well as pointing you
> >> to
> >> the tech report.
> >>
> >> T
> >>
> >>
> >> On 12 Mar 2007, at 21:36, Xuelin Cui wrote:
> >>
> >>> hi Steve:
> >>>
> >>> Thanks for reply
> >>>
> >>> But could you please forward my email to Christian? I am reading
> >>> the technique report. Those questions are exactly the questions
> >> on
> >>> the technique report.
> >>>
> >>> Thanks
> >>>
> >>> Xuelin
> >>>
> >>> ****************************************
> >>> Xuelin Cui
> >>> Department of Electrical Engineering
> >>> University of Hawaii-Manoa
> >>> Honolulu HI 96822
> >>>
> >>> Tel: 1-808-349-0983
> >>> Email: [log in to unmask]
> >>> ****************************************
> >>>
> >>> ----- Original Message -----
> >>> From: Steve Smith <[log in to unmask]>
> >>> Date: Monday, March 12, 2007 7:34 am
> >>> Subject: Re: [FSL] some theoretical questions on MELODIC
> >>> To: [log in to unmask]
> >>>
> >>>> Hi,
> >>>>
> >>>> As well as Christian's main techrep, you should read the basic
> >>>> intro
> >>>> to ICA at:
> >>>> http://www.fmrib.ox.ac.uk/analysis/techrep/tr01mj2/tr01mj2.pdf
> >>>>
> >>>>
> >>>> On 12 Mar 2007, at 09:34, Xuelin Cui wrote:
> >>>>
> >>>>> hi Christian:
> >>>>>
> >>>>> I have a question on equation 5 in you technique report 2.
> >>>>>
> >>>>> Equation 5 seems to be the maximum likelihood estimation of
> >>>> mixing
> >>>>> matrix. It is:
> >>>>> A_ml=U_q*(lamda_q-sigma^2*I)^1/2*Qt
> >>>>> Is U_q the eigenvector matrix directly solved from the 2D fMRI
> >>>> data
> >>>>> by PCA?
> >>>>
> >>>> Nearly: it is the top q eigenvectors from the initial data PCA.
> >>>>
> >>>>> If so, should each of the column vector in U_q be orthogonal?
> >>>>
> >>>> Yes.
> >>>>
> >>>>> Also, I dont really figure out that where does the Q matrix come
> >>>>> from. Since it is a rotational matrix, each column of it should
> >>>> be
> >>>>> orthogonal too, right? Why we need Q here?
> >>>>
> >>>> Q is the final ICA rotation within the space produced by the PCA.
> >>>> WIthout Q you would just have PCA.
> >>>>
> >>>> Steve.
> >>>>
> >>>>
> >>>>>
> >>>>> Thanks a lot in advance
> >>>>>
> >>>>> Xuelin
> >>>>>
> >>>>> ****************************************
> >>>>> Xuelin Cui
> >>>>> Department of Electrical Engineering
> >>>>> University of Hawaii-Manoa
> >>>>> Honolulu HI 96822
> >>>>>
> >>>>> Tel: 1-808-349-0983
> >>>>> Email: [log in to unmask]
> >>>>> ****************************************
> >>>>>
> >>>>> ----- Original Message -----
> >>>>> From: Christian Beckmann <[log in to unmask]>
> >>>>> Date: Tuesday, March 6, 2007 5:06 pm
> >>>>> Subject: Re: [FSL] some theoretical questions on MELODIC
> >>>>> To: [log in to unmask]
> >>>>>
> >>>>>> Xuelin,
> >>>>>>
> >>>>>> all of these questions are readily answered in the technical
> >>>>>> report
> >>>>>> http://www.fmrib.ox.ac.uk/analysis/techrep/tr02cb1/tr02cb1.pdf
> >>>>>>
> >>>>>>> 1. Is PCA applied to the data before ICA is applied? (to
> >>>>>> decrease
> >>>>>>> the dimentionality)
> >>>>>> Yes, the maximum likelihood estimate is given by a rotated PCA
> >>>>>> solution (equation 5 in the TR)
> >>>>>>
> >>>>>>> 2. If PCA is applied as a preprocessing, where are those
> >>>>>> principal
> >>>>>>> components fed into?(put it in this way: After PCA applied, we
> >>>>>> have
> >>>>>>> a matrix E of some eigenvectors, is E same with X? where X=MS,
> >>>>>> X:
> >>>>>>> mixed information, M: mixing matrix, S: source)
> >>>>>> Nope, PCA uses the Eigenvectors of the data covariance
> matrix of
> >>>>>> X,
> >>>>>> see text after equation 5
> >>>>>>
> >>>>>>> 3: What criterion is used to extract those ICs by MELODIC?
> >>>>>>> (minimize the negentropy?)
> >>>>>> Approximations to neg-entropy, see text and equation 12
> >>>>>>
> >>>>>>> 4. What on earth are those ICs, which are extracted by
> MELODIC?>>>>>> Projections of the data which are maximally non-
> Gaussianity - see
> >>>>>> text and equation 12. You might find the section on
> 'uniqueness'>>>>>> interesting, too
> >>>>>>
> >>>>>> hope this helps
> >>>>>> Christian
> >>>>>>
> >>>>>>> Thanks a lot in advance
> >>>>>>>
> >>>>>>> Xuelin
> >>>>>>>
> >>>>>>> ****************************************
> >>>>>>> Xuelin Cui
> >>>>>>> Department of Electrical Engineering
> >>>>>>> University of Hawaii-Manoa
> >>>>>>> Honolulu HI 96822
> >>>>>>>
> >>>>>>> Tel: 1-808-349-0983
> >>>>>>> Email: [log in to unmask]
> >>>>>>> ****************************************
> >>>>>>
> >>>>>> --
> >>>>>> Christian F. Beckmann
> >>>>>> Oxford University Centre for Functional
> >>>>>> Magnetic Resonance Imaging of the Brain,
> >>>>>> John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
> >>>>>> Email: [log in to unmask] -
> >>>>>> http://www.fmrib.ox.ac.uk/~beckmann/ Phone: +44(0)1865 222551
> >>>>>> Fax: +44(0)1865 222717
> >>>>>>
> >>>>
> >>>>
> >>>> ---------------------------------------------------------------
> --
> >> ---
> >>>> ----
> >>>> ---
> >>>> Stephen M. Smith, Professor of Biomedical Engineering
> >>>> Associate Director, Oxford University FMRIB Centre
> >>>>
> >>>> FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
> >>>> +44 (0) 1865 222726 (fax 222717)
> >>>> [log in to unmask] http://www.fmrib.ox.ac.uk/~steve
> >>>> ---------------------------------------------------------------
> --
> >> ---
> >>>> ----
> >>>> ---
> >>>>
> >>
>
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