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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 >>>> ----------------------------------------------------------------- >> --- >>>> ---- >>>> --- >>>> >>