Scattering order formulation

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Implement SOF (Born series) as a iterative solver (with controlled number
of iterations). It can be used, e.g., to simulate RDG results.

Original issue reported on code.google.com by yurkin on 24 Dec 2008 at 7:26

• Blocked on: #111

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Original comment by yurkin on 4 Sep 2010 at 2:35

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RDG results should be possible to imitate by '-maxiter 0 -init_field inc'. The 
problem is that maxiter currently requires a positive argument (and produces a 
warning in the end of iterations).

So a way to go is, probably, to allow '-maxiter 0' globally (why not?), and 
remove the warning (convergence not reached) if a special iterative solver is 
used (SOF, to be implemented). Another question is whether SOF should use '-eps 
...' or not. I.e. if I want 5 orders of scattering, but the result converge to 
1e-5 after 3, should ADDA stop? Then, if we keep everything as is, there should 
be a note that pure SOF requires '-eps 100' or something... May be add a 
separate argument, like '-eps none' not to check convergence at all (can be 
possible only in combination with maxiter - actually this can be the perfect 
reason to turn off not-converged warnings).

Original comment by yurkin on 29 Jul 2014 at 5:18

• Now blocked on: #111

[myurkin]

I am not sure what will happen, if one uses -maxiter 1. For some iterative solvers that may be the same as running one scattering-order iteration (need further analysis). Then combining it with -store_int_field and -init_field read ... iteratively can lead to the complete scattering-order series.