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NestList in 12.1/12.2 is 10x slower than 11.3/12.0

Mathematica Asked on August 18, 2021

Are there any configurations to fix it?

Test code:

Clear["`*"];
fun[matrix_, n_, β_, {i_, j_}] := Block[{p, E1, mat = matrix},
   p = matrix[[i, j]];
   E1 = -Total[
      p {matrix[[Mod[i - 1, n, 1], j]], matrix[[Mod[i + 1, n, 1], j]],
         matrix[[i, Mod[j - 1, n, 1]]], 
        matrix[[i, Mod[j + 1, n, 1]]]}];
   mat[[i, j]] = 
    If[E1 >= 0, -p, 
     RandomChoice[{Exp[2 E1 β], 1 - Exp[2 E1 β]} -> {-p, 
        p}]];
   mat
   ];
Ising[β_, n_, step_]:= 
  Block[{mat = RandomChoice[{1, -1}, {n, n}], f},
   f := RandomInteger[{1, n}, 2];
   NestList[fun[#, n, β, f] &, mat, step]
   ];
ClearSystemCache[];
Mean[First /@ 
  Table[AbsoluteTiming[
    fun[RandomChoice[{1, -1}, {100, 100}], 100, 0.8, 
      RandomInteger[{1, 100}, 2]];], 3746]]
Ising[0.8, 100, 10^5]; // AbsoluteTiming

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