HI - I think this is similar to the query I answered a few days ago -
it is possible that the first two contrasts are illegal because
randomise can't generate permutations on a [1 0...] contrast when EV1
is all 1s (that's why we have the "-1" sign flipping option in
randomise).
But Matthew/Tom can confirm whether this is correct.
Cheers.
On 11 Nov 2008, at 21:13, Melissa Lopez-Larson wrote:
> Hello,
>
> I am attempting to compare 2 subject groups in vbm and I wanted to
> add age as another
> EV. I demeaned the data and set my design matrix and design
> contrast but get the error
> below. I have tried to change my matrix many times in the GLM and
> can not figure out
> what I am doing wrong.
> Thanks,
> Melissa
>
> /NumWaves 2
> /NumPoints 21
> /PPheights 1 1
> /Matrix
> 1 0 3.87 0
> 1 0 -0.63 0
> 1 0 3.26 0
> 1 0 2.75 0
> 1 0 -2.35 0
> 1 0 1.32 0
> 1 0 -1.41 0
> 1 0 0.79 0
> 1 0 -1.83 0
> 1 0 0.17 0
> 0.0 1.0 0 2.63
> 0.0 1.0 0 3.55
> 0.0 1.0 0 -3.76
> 0.0 1.0 0 -2.37
> 0.0 1.0 0 -0.59
> 0.0 1.0 0 -1.37
> 0.0 1.0 0 1.24
> 0.0 1.0 0 -1.99
> 0.0 1.0 0 -0.41
> 0.0 1.0 0 0.67
> 0.0 1.0 0 -1.83
>
>
>
> and my design.con as:
> /NumWaves 2
> /NumContrasts 4
> /PPheights 1 1
> /Matrix
> 1 0 0 0
> 0 1.0 0 0
> 1.0 -1.0 0 0
> -1.0 1.0 0 0
>
>
> However, I get the following error after the permutation have run:
>
> An exception has been thrown
> Runtime error:- detected by Newmat: matrix is singular
>
> MatrixType = Crout # Rows = 2; # Cols = 2
> Trace: Crout(lubksb); GeneralSolvI; InvertedMatrix::Evaluate.
>
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
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