SwE and TBSS

[Yael Coldham]

Hi,

I am working with a dataset with 2 groups (treatment, control) and 4 timepoints, with missing data. I'm using FSL's SWE tool (modified, as I have 30-50 participants per group per TP).
I'm investigating WM changes and have run TBSS on all participants. I'm using a TBSS mask based on the 4D matrix of all participants' data.

I was able to run SWE to detect time*group interactions between every pair of TPs (tp1-tp2, tp2-tp3, tp3-tp4), with this design.con:
/NumWaves 8
/NumContrasts 6

/Matrix
0 0 0 0 0 1 0 0
0 0 0 0 0 -1 0 0
0 0 0 0 0 -1 1 0
0 0 0 0 0 1 -1 0
0 0 0 0 0 0 -1 1
0 0 0 0 0 0 1 -1

but when I try getting the omnibus F interaction with the following fts matrix:
/NumWaves 6
/NumContrasts 6

/Matrix
1 0 1 0 1 0

with the command:

swe -i "all_FA_skeletonised_4D.nii.gz" -o "swe_results" -d "design.mat" -t "design.con" -f "design.fts" -s "design.sub" -m "common_skeleton_mask.nii.gz" --modified --wb -n 999 -T --uncorrp --logp -R

I get the following error message:
Setting up the model: done Loading data: done Checking the inputs: done Computing original equivalent scores: warning: solve(): system is singular; attempting approx solution ** On entry to DLASCL parameter number 4 had an illegal value ** On entry to DLASCL parameter number 4 had an illegal value ERROR: Program failed: solve(): solution not found any thoughts what could have gone wrong here?

Many thanks
Yael