probably something wrong with your stimulus schedule (paradigm). Can you send the X.mat (or Xtmp.mat)?

On 2/28/2023 12:12 PM, Caspar M. Schwiedrzik wrote:

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Hi! I am running into an issue with fast_selxavg3b. I am attempting a first level PPI analysis.

The command is mkanalysis-sess -fsd bold -native -delay -2/2 -notask -TR 2 -polyfit 6 -analysis [xxx] -funcstem [xxx] -runlistfile mooneyppi.list -nuisreg motion.dat 6 -tpef tpef_dvars.dat -acfbins 5 -acffwhm 0 -mask [xxx] -force -nuisreg juice.dat 1 -nuisreg fixation.dat 1 -taskreg ppi.dat 4

I get the following error:

GLS Residual Pass   run 1    t= 0.0 Error using chol Matrix must be positive definite.

Error in fast_selxavg3b (line 942) Wseg = inv(chol(toeplitz(acfrun))');

Before that, I am getting several warnings of this kind:

...

In fast_selxavg3b (line 895)

Warning: Matrix is singular, close to singular or badly scaled. Results may be inaccurate.

A few of them, but not run 1, have RCOND = NaN.

This is with versions 7.2 and 5.3. I found one previous conversation on the mailing list regarding this error in the context of a resting state analysis, but no conclusion. Any advice would be appreciated. Thanks! Caspar

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