> That's because of noise normalization - for the free orientation solution
> noise normalization calculates a sum across the three dimensions (line 171),
> and then square root is taken of that sum, whereas when the orientation is
> fixed the sum isn't calculated, so only noise in the normal direction is
> taken into account and therefore it can be much smaller than for the free
> orientation case.

then the pick of the normal should be done avec the noise normalization.

> Come to think of it it's more than just a question of numerical
> problems... when free orientation is chosen the final result is:
> norm_of_activity_vector / norm_of_noise_vector, whereas when normal
> orientation is picked the result is activity_in_normal_direction /
> noise_in_normal_direction and if most of the noise is in a direction
> different than the normal direction, then the norm_of_noise_vector will be
> much higher then noise_in_normal_direction. Makes sense?

ok. But then take a look at the minimum_norm code. You raise a doubt.
I would have picked the normal after the xyz noise normalization.

> In any case, when normal orientation is picked after noise normalization,
> the difference disappears. So maybe that's where the orientation should be
> picked? I put it before noise normalization for consistency with
> minimum_norm... but I don't know that code too well, so maybe it's a
> slightly different issue here than there and there's no point in maintaining
> consistency...?

@mluessi any opinion?

@rgoj : have a look at the minimum_norm code