Dear Ken,
sorry for my first (empirical) doubts, you were actually really close to
the right formula which is (see below the corrected process to get there):
M3=MM*inv(M2)*M1;
If anybody is interested, I will right a short matlab code to compute
this transformation and save the .mat files properly.
Thank you very much for your help.
Nicolas.
> Sorry- I did not carefully read Johns reply. I think he is saying
> that without
> a mat file, a matrix that is not identical to eye(4) is generated as a
> default
> space. To get around this, lets call this matrix MM for "mystery
> matrix", and
> we want to solve for M3 so that
>
> MM * vc_2 = M3 * vc_1
>
> The "mystery matrix" can be found with spm_get_space, which is in the
> recent
> updates to spm2.
>
> So, from before:
>
> vc_2 = inv(M2) * M1 * vc_1
Ok. And simply left multiplying by MM leads to the exact formula.
> inv(MM) * MM * vc_2 = inv(M2) * M1 * vc_1
This line is Ok.
> MM * vc_2 = inv(MM) * inv(M2) * M1 * vc_1
The Pb is there => you should have multiplied by MM.
> M3 = inv(MM) * inv(M2) * M1
M3=MM*inv(M2)*M1
|