Summary

Mathematica 11.0 code

\[Lambda] = 10.;
k0 = (2 \[Pi])/\[Lambda];
\[Alpha] = 4/(k0^2 I);
\[Sigma] = (k0^3 Norm[\[Alpha]]^2)/4 // N
G[r_] := N[I/4 HankelH1[0, k0 Norm[r] ]];
dim = 100; (*Number of scatterers*)

rs = Table[{RandomReal[{-\[Lambda]*20, \[Lambda]*20}], 
    RandomReal[{\[Lambda]*5, \[Lambda]*15}]}, {dim}];

(**)
ns = 
  40; (*number of sources, i.e. number of degrees of freedom we can control*)
s[r_] := 
  Table[E^(I k0 Norm[r - {j, 0}])/
   Norm[r - {j, 
      0} ], {j, -\[Lambda]*10, \[Lambda]*10, (\[Lambda]*20)/(ns - 1)}];
E0 = Table[
   N[s[rs[[j]] ]], {j, 1, dim}]; (*source field on each scatterer*)

iME = Inverse@Table[
      If[k == j, 1, \[Alpha] k0^2 G[rs[[j]] - rs[[k]] ] ]
    , {j, 1, dim}, {k, 1, dim}];
Es = Table[
   iME.E0[[All, j]], {j, 1, ns}]; (*Total field on each scatterer*)
Etot = Table[(*s[{x,y}][[
   i]]+*)\[Alpha] k0^2 Sum[
     G[{x, y} - rs[[j]] ] Es[[i, j]], {j, 1 dim}], {i, 1, 
    ns}, {x, -\[Lambda]*10, \[Lambda]*10, 2}, {y, 2, \[Lambda]*20 + 2,
     2}]; (*Total field everywhere (this is the part that takes ages to compute)*)
(*If s[{x,y}][[j]] is commented out, only the scattered  field is computed.*)
target = {60, 65};
iterative = 
  Table[If[j == k, Etot[[j, target[[1]], target[[2]] ]] E^(I \[Phi]), 
    Etot[[j, target[[1]], target[[2]] ]] ], {k, 1, ns}, {j, 1, ns}];
\[Delta]\[Phi] = 
 Table[FindMaximum[Abs[Total@iterative[[j]] ]^2, {\[Phi], 0}][[2, 1, 
   2]], {j, 1, ns}];
sourcepos = 
  Table[{j, 1}, {j, -\[Lambda]*10, \[Lambda]*10, (\[Lambda]*20)/(
    ns - 1)}];
p1 = Table[
  GraphicsRow[{
    ArrayPlot[
     Reverse@Transpose@(
       Abs[Sum[Etot[[j]] E^(I \[Delta]\[Phi][[j]]), {j, 1, i}] + 
         Sum[Etot[[j]], {j, i + 1, ns}] ]^2) , 
     DataRange -> {{-\[Lambda]*10, \[Lambda]*10}, {2, \[Lambda]*20 + 
         2}}, ColorFunction -> "AvocadoColors", ImageSize -> Large, 
     Epilog -> {PointSize -> Medium, White, PointSize[0.02], 
       Point[rs], Red, Thickness[0.007], 
       Circle[{(target[[1]] - 1)*2 - \[Lambda]*10, (target[[2]] - 
             1)*2 + 2}, 8]
       ,
       Table[
        Line[{{sourcepos[[j, 1]] - \[CapitalDelta]s/
            2, -\[Delta]\[Phi][[j]] + 
            2}, {sourcepos[[j, 1]] + \[CapitalDelta]s/
            2, -\[Delta]\[Phi][[j]] + 2}}]
        , {j, 1, i}],
       Table[
        Line[{{sourcepos[[j, 1]] - \[CapitalDelta]s/2, 
           2}, {sourcepos[[j, 1]] + \[CapitalDelta]s/2, 2}}]
        , {j, i + 1, ns}]
       }]
    ,
    ListPlot[
     Abs[Sum[
        Etot[[j, All, target[[2]]]] E^(I \[Delta]\[Phi][[j]]), {j, 1, 
         i}] + Sum[Etot[[j, All, target[[2]]]], {j, i + 1, ns}] ]^2 , 
     Joined -> True, PlotRange -> {0, maxopt}, Axes -> False, 
     Frame -> True, FrameTicks -> None, PlotStyle -> {Thick, Green}]
    }],
  {i, 1, ns - 1, 1}];
ListAnimate[p1]

Licensing

I, the copyright holder of this work, hereby publish it under the following license:

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The person who associated a work with this deed has dedicated the work to the public domain by waiving all of their rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. You can copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission. http://creativecommons.org/publicdomain/zero/1.0/deed.enCC0Creative Commons Zero, Public Domain Dedicationfalsefalse

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This file, which was originally posted to https://twitter.com/j_bertolotti/status/1063490538740072449, was reviewed on 17 November 2018 by reviewer Ronhjones, who confirmed that it was available there under the stated license on that date.