Dear All,
I am a beginner of SPM8. I am taking "DEM_demo_DCM_LAP.m" as an example to simulate fMRI data without using any real measured fMRI data and to learn how to inversely estimate that connectivity matrix.
To simulate the data, I need to provide the intrinsic matrix (A). In my understanding, the off-diagonal elements should be correlation coefficients while the diagonal elements should be set as -1. Am I right?
so given a non-singular correlation coefficient matrix A=[ 1 0.8 0.8 0.8 0.8;
0.8 1 0.64 0.64 0.64;
0.8 0.64 1 0.64 0.64;
0.8 0.64 0.64 1 0.64;
0.8 0.64 0.64 0.64 1],
I just replaced all 1s with -1 to fill in the intrinsic matrix. However, I got a lot of warnings saying the matrix is singular. Could you please tell me how to set the intrinsic matrix according to this case? Any suggestion will be much appreciated.
Regards,
Wang C.
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