No, he is, as I write, undergoing emergency surgery to have his
appendix removed and will be out of action for a few days.
Hopefully the technical reports, including the basic background one
that I emailed about, can help give a good background on the ICA
maths - read them carefully and then hopefully by the time Christian
is back with us you'll be an ICA expert!
Steve,
On 12 Mar 2007, at 22:23, Xuelin Cui wrote:
> 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
>>>>>> ---------------------------------------------------------------
>> --
>>>> ---
>>>>>> ----
>>>>>> ---
>>>>>>
>>>>
>>
------------------------------------------------------------------------
---
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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