diff --git a/matlab/isauxiliary.m b/matlab/isauxiliary.m
new file mode 100644
index 000000000..a3788dde0
--- /dev/null
+++ b/matlab/isauxiliary.m
@@ -0,0 +1,68 @@
+function b = isauxiliary(var, type)
+
+% Returns true if var is an auxiliary variable.
+%
+% INPUTS
+% - var       [string]    Name of the variable.
+% - type      [integer]   Type of auxiliary variable.
+%
+% OUTPUTS
+% - b         [logical]
+%
+% REMARKS
+%
+% Types for auxiliary variables are as follows:
+%  
+%   -  0,    Lead on endogenous variable (substitute for endo leads >= 2)
+%   -  1,    Lag on endogenous variable (ubstitute for endo lags >= 2)
+%   -  2,    Lead on exogenous variable  (ubstitute for exo leads >= 1)
+%   -  3,    Lag on exogenous variable (substitute for exo lags >= 1)
+%   -  4     Expectation (substitute for Expectation Operator)
+%   -  5,    Diff forward (substitute for the differentiate of a forward variable)
+%   -  6,    Multipliers for FOC of Ramsey Problem
+%   -  7,    Variable for var_model with order > abs(min_lag()) present in model
+%   -  8,    Variable for Diff operator
+%   -  9,    Lag on Diff
+%   - 10,    Unary operator (log, exp)
+
+% Copyright (C) 2018 Dynare Team
+%
+% This file is part of Dynare.
+%
+% Dynare is free software: you can redistribute it and/or modify
+% it under the terms of the GNU General Public License as published by
+% the Free Software Foundation, either version 3 of the License, or
+% (at your option) any later version.
+%
+% Dynare is distributed in the hope that it will be useful,
+% but WITHOUT ANY WARRANTY; without even the implied warranty of
+% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+% GNU General Public License for more details.
+%
+% You should have received a copy of the GNU General Public License
+% along with Dynare.  If not, see <http://www.gnu.org/licenses/>.
+
+global M_
+
+b = false;
+
+id = find(strcmp(var, M_.endo_names));
+
+if isempty(id)
+    return
+end
+
+if id<=M_.orig_endo_nbr
+    return
+else
+    b = true;
+    if nargin<2
+        return
+    end
+end
+
+auxinfo = M_.aux_vars(get_aux_variable_id(id));
+
+if ~isequal(auxinfo.type, type)
+    b = false;
+end
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