Dear all,
I am encountering a few problems with a DCM analysis in DCM10/SPM8.
As already reported by others, DCM10 model estimation seems to take comparably
much longer to run than in previous DCM versions.
This is particularly problematic for the BMS approach we would like to take,
with a model space of 108 models in 16 subjects. Estimation of one single model
takes hours to almost 1 day, even on the most powerful 64bit Sun server with 8
processors and 16GB RAM that we have in our lab, compared to minutes or max. 1-2
hours in previous software versions.
A second problem is memory utilization: DCM10 model estimation has failed on all
32bit calculators I have tested so far, with an out of memory error message
(running matlab 2008a). This is less of a problem with 64bit calculators, but
with some models I nevertheless get an out of memory error message.
The last and most critical problem is that with 4 models out of 128, after
several EM steps I get a "matrix is close to singular" warning and model
estimation never happens to converge. As a matter of fact the CPU seems to be
completely soaked up by the process and to become completely unusable. The only
solution then is to shut down the power supply and reboot.
I do not know whether this problem is model or subject dependent, as I could
only test one subject up to now.
There may be specific problems related to the configuration of these particular
4 models, but I am not able to identify any: the model space is simply generated
by allowing or not allowing input or modulatory effects on connections.
Any help is greatly appreciated.
Best wishes,
Marco
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Marco Tettamanti, Ph.D.
San Raffaele Scientific Institute
Via Olgettina 58
I-20132 Milano, Italy
Tel. ++39-02-26434888
Fax ++39-02-26434892
Email: [log in to unmask]
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