During 3D variability analysis, at each iteration two diagnostic parameters are printed out to the log file (see below) - “min-ev” and “num bad voxels”. What are these parameters, and are they useful for diagnosing when something is going wrong during the analysis? If so what are reasonable ranges?
These are not really very easy to interpret (and dont have any bearing on the results) but they are part of the new process of fixing the “streaking” issue that was previously happening. The num bad voxels in particular is reporting the number of voxels detected where the values computed are within numerical tolerance of zero. Those are now automatically set to zero, so if you do see a non-zero number of bad voxels, it’s nothing to worry about as long as you don’t see streaking in the results.
In v2.12.4 I changed some of the default params of 3D var further, and it now works really well in most cases - you can solve 6 or more modes without streaking, even on smaller datasets.