further simplifications related to AR matrices

src/ExprNode.cc

@@ -5872,21 +5872,10 @@ BinaryOpNode::fillAutoregressiveRow(int eqn, const vector<int> &lhs, map<tuple<i
                 }
               if (vid >= 0)
                 {
-                  int vidineq = vid;
-                  while (datatree.symbol_table.isAuxiliaryVariable(vid))
-                    try
-                      {
-                        vid = datatree.symbol_table.getOrigSymbIdForAuxVar(vid);
-                      }
-                    catch (...)
-                      {
-                        break;
-                      }
-
-                  if (vidineq != vid)
+                  if (datatree.symbol_table.isDiffAuxiliaryVariable(vid))
                     {
-                      vid = datatree.symbol_table.getOrigSymbIdForDiffAuxVar(vidineq);
-                      lag = -datatree.symbol_table.getOrigLeadLagForDiffAuxVar(vidineq);
+                      lag = -datatree.symbol_table.getOrigLeadLagForDiffAuxVar(vid);
+                      vid = datatree.symbol_table.getOrigSymbIdForDiffAuxVar(vid);
                     }
 
                   if (find(lhs.begin(), lhs.end(), vid) == lhs.end())

src/SymbolTable.cc

@@ -1091,6 +1091,18 @@ SymbolTable::isAuxiliaryVariableButNotMultiplier(int symb_id) const
   return false;
 }
 
+bool
+SymbolTable::isDiffAuxiliaryVariable(int symb_id) const
+{
+  for (const auto & aux_var : aux_vars)
+    if (aux_var.get_symb_id() == symb_id &&
+        (aux_var.get_type() == AuxVarType::diff
+         || aux_var.get_type() == AuxVarType::diffLag
+         || aux_var.get_type() == AuxVarType::diffLead))
+      return true;
+  return false;
+}
+
 set<int>
 SymbolTable::getOrigEndogenous() const
 {

src/SymbolTable.hh

@@ -408,6 +408,8 @@ public:
   bool isAuxiliaryVariable(int symb_id) const;
   //! Is a given symbol an auxiliary variable but not a Lagrange multiplier
   bool isAuxiliaryVariableButNotMultiplier(int symb_id) const;
+  //! Is a given symbol a diff, diff lead, or diff lag auxiliary variable
+  bool isDiffAuxiliaryVariable(int symb_id) const;
   //! Get list of endogenous variables without aux vars
   set <int> getOrigEndogenous() const;
 };