The implementation is slightly different to that described in Numerical
Recipes. "sc" is a tolerance for stopping the optimization. If the
changes in the parameters decrease below these values, then the
registration will stop searching and continue on to the next step. The
"xi" variable simply contains the directions to begin searching along,
and is a sort of initial step size.
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]]
On Behalf Of ulas bagci
Sent: Saturday, April 07, 2007 6:17 PM
To: [log in to unmask]
Subject: [SPM] Co-registration, what is special about sc?
in coregistration code( spm_coreg and spm_powell)
do you know that what is the meaning of
xi = diag(sc*20); where sc is defined as follows:
sc=[0.02 0.02 0.02 0.001 0.001 0.001 0.01 0.01 0.01 0.001 0.001 0.001]';
in powell optimization xi should show the direction of search, as
default it is identity matrix( eye(6) in this case), but in spm code, it
is taken multiple of tolerance with 20. Have you got any ideas about
this initialization? When I enter manually, identity in replace to xi,
co-registration result is not promising.
thanks in any advance reply.
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