Dear SPMers,
I have a problem with estimating the parameters of a dynamical model. I have a DCM with 3 areas and 1 input, and I'm trying to estimate connection parameters with SPM. However, the Fisher scoring scheme for estimating the hyperparameters controlling the observation noise covariance is oscillating between zero and one (the log of the hyperparams, denoted by h in spm_nlsi_GN.m, are taking values near 0 and -1500 in successive iterations respectively). I tried with several connection patterns, intrinsic and modulatory, I get the same all the time.
When I consider noise covariance known (fix the hyperparameters and do not update them by the Fisher scheme), the iteration of the E-step of the parameter estimation runs without errors, but I don't know how much I could rely on such results, I'm assuming not really.
Could you give me a hint about what direction should I look for the source of the issue?
Thank you very much,
Mihály
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