This directory contains transmission tomography reconstruction algorithms,
mostly for monoenergetic sources, e.g., PET and SPECT transmission scans.
The routines may also be useful for X-ray CT but be aware that CT
does not satisfy exactly the Poisson statistical model assumed here.
The ordered-subsets (OS) algorithms are not monotonic (with nsubset > 1).
A possible modification would be to use the fast precomputed denominator
and then check the cost function each iteration and if the cost function
goes the wrong direction then backtrack to 1-subset case with optimal
curvatures. But for OS methods, checking the cost function is expensive
since we would have to perform reprojection.
The recommended routine here is: tpl_os_sps.m (see tpl_os_sps_test.m)