Fix MCP solver in the presence of multiple complementarity conditions

The solver relies on a reordering of equations (eq_index) so that reordered
equations appear at the index of the endogenous to which they are associated
through the complementarity condition.

However, this reordering could be computed incorrectly in the presence of
multiple complementarity conditions (technically, eq_index was not necessarily
a permutation).

(cherry picked from commit 1fea7f3e)

matlab/lmmcp/get_complementarity_conditions.m

@@ -12,7 +12,7 @@ function [lb,ub,eq_index] = get_complementarity_conditions(M_,ramsey_policy)
 %                                from complementarity setup used in
 %                                perfect_foresight_mcp_problem.m
 
-% Copyright © 2014-2018 Dynare Team
+% Copyright © 2014-2024 Dynare Team
 %
 % This file is part of Dynare.
 %
@@ -60,7 +60,9 @@ for i=1:size(etags,1)
                 error('Complementarity condition %s: variable %s is not recognized', etags{i,3}, strtrim(str(1:kop-1)))
             end
             ub(k) = str2num(str(kop+1:end));
-            eq_index(eq_nbr) = k;
+            swapped_eq_nbr = find(eq_index == eq_nbr);
+            assert(length(swapped_eq_nbr) == 1);
+            eq_index(swapped_eq_nbr) = eq_index(k);
             eq_index(k) = eq_nbr;
         else
             kop = strfind(etags{i,3},'>');
@@ -70,7 +72,9 @@ for i=1:size(etags,1)
                     error('Complementarity condition %s: variable %s is not recognized', etags{i,3}, strtrim(str(1:kop-1)))
                 end
                 lb(k) = str2num(str(kop+1:end));
-                eq_index(eq_nbr) = k;
+                swapped_eq_nbr = find(eq_index == eq_nbr);
+                assert(length(swapped_eq_nbr) == 1);
+                eq_index(swapped_eq_nbr) = eq_index(k);
                 eq_index(k) = eq_nbr;
             else
                 error('Complementarity condition %s can''t be parsed',etags{i,3})