gradient descent notebook

[KrisThielemans]

the PET recon has a funny line

Also, it is called gradient descent, but it is actually ascending due to some minus signs. Better to switch the sign in the PET, but keep it for MR and CT.

[evgueni-ovtchinnikov]

@KrisThielemans Which notebook are you referring to?

SIRF-Exercises notebook ML_reconstruction compares OSEM with gradient ascent, and so far as I remember, other PET notebooks in SIRF-Exercises do not deal with gradient descent too.

[KrisThielemans]

Synergistic/gradient_descent_mr_pet_ct.ipynb. No need to fix this now though. Next release!

[KrisThielemans]

b6b0d6b edited the notebook a bit to warn people about the confusion on signs.

[KrisThielemans]

@ckolbPTB should we move this notebook to Introductory in the next release? There isn't anything "synergistic" here really, and it nicely follows up from the other ones in that folder.

[KrisThielemans]

@ckolbPTB what do you think about moving this to Introductory?

[KrisThielemans]

@evgueni-ovtchinnikov would you have time to change the sign here and adjust?

[KrisThielemans]

currently the "ascent" is addressed by updating text in the notebook. This is good enough for 3.5. We'll multiply the PET objective function with -1 and descend in the next version

[KrisThielemans]

Move now completed.

The only thing remaining here is the strange line in the PET reconstructions.