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Dear experts,
I’m running into an error when running selxavg3. It says the design is ill-conditioned. I’m a bit stuck, because the same pipeline works in most subjects, but not all. Also, if I exchange the functional scan (f.nii.gz) with a scan from a working session of the same subject (same number of volumes etc.) I don’t get any errors. I’m grateful for any advice that helps to track down the mistake I’m doing.
Here the content of the selxavg3.log file: cd /home/hector/SENS_MAPPING_BLOCK/sessions /opt/software/freesurfer/fsfast/bin/selxavg3-sessbc -s HEC_035_1 -analysis MPBDandefs_orig_lhrh_revd11.5_sm2.lh -no-preproc -fwhm -force Found 42449/139130 (30.5) voxels in mask Creating Design Matrix ... creation time = 0.004 sec DoMCFit = 1 ntptot = 500, nX = 33, DOF = 467 XCond = 2.63784e+16 (normalized) ERROR: design is ill-conditioned
Before the error it gives a warning that the design matrix is singular or badly scaled: [Warning: Matrix is close to singular or badly scaled. Results may be inaccurate. RCOND = 1.271035e-17.] [> In fast_selxavg3bc (line 318)] norm(inv(XtX),2) = [14601308845709730.0] Saving X matrix to /home/hector/SENS_MAPPING_BLOCK/sessions/HEC_035_1/bold/MPBDandefs_orig_lhrh_revd11.5_sm2.lh/Xtmp.mat XCond = 2.63784e+16 (normalized) ERROR: design is ill-conditioned
ERROR: fast_selxavg3bc() failed\n
Many thanks in advance, Martin