optimize sample thickness during multi-slice ptycho reconstruction

[yijiang1]

I think it's possible to make use of existing code to optimize sample thickness (delta_z) during GPU_MS reconstruction.

Functions worth checking out:
+GPU_MS/LSQML.m
+GPU_MS/private/gradient_NF_propagation_solver.m
+ML_MS/gradient_ptycho_MS.m
+ML_MS/calc_ms_grad.c

[zhenchen16]

I noticed this after I read the extended depth of field paper in 2016. They mentioned this as a new optimzation direction. I'm not sure whether it's robust enough. Worth trying though.

[yijiang1]

Another paper on this topic: https://doi.org/10.1364/OL.389492