function plan = flip_plan(plan, exogenous, endogenous, expectation_type, date, value)
% Adds to the forecast scenario a conditional forecast shock (the path of an endogenous variable is constrained and the values compatible values of the related exogenous variable will be compued)
%
% INPUTS
%  o plan                 [structure]       A structure describing the different shocks and the implied variables, the date of the shocks and the path of the shock (forecast scenario).
%                                           The plan structure is created by the functions init_plan, basic_plan and flip_plan
%  o exogenous            [string]          A string containing the name of the endogenous variable with a constrained path.
%  o endogenous           [string]          A string containing the name of the exogenous. This exogenous variable will be en endogenous variable when the conditional forecast will be perform.
%  o expectation_type     [string]          A string indicating the type of expectation: 'surprise' for an unexpected shock, and 'perfect_foresight' for a perfectly anticpated shock.
%  o date                 [dates]           The period of the shock
%  o value                [array of double] A vector of double containing the constrined path on the endogenous variable
%
%
% OUTPUTS
%  plan                   [structure]        Returns a structure containing the updated forecast scenario.
%
%
% Copyright (C) 2013-2014 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/>.
  if ~ischar(expectation_type) || size(expectation_type,1) ~= 1
      error(['in flip_plan the fourth argument should be a string containing the simulation type (''perfect_foresight'' or ''surprise'')']);
  end
  exogenous = strtrim(exogenous);
  ix = find(strcmp(exogenous, plan.endo_names));
  if  isempty(ix)
      error(['in flip_plan the second argument ' exogenous ' is not an endogenous variable']);
  end;
  endogenous = strtrim(endogenous);
  iy = find(strcmp(endogenous, plan.exo_names));
  if  isempty(iy)
      error(['in flip_plan the third argument ' endogenous ' is not an exogenous variable']);
  end;
  sdate = length(date);
  if sdate > 1
      if date(1) < plan.date(1) || date(end) > plan.date(end)
          error(['in flip_plan the fifth argument (date='  date ') must lay inside the plan.date ' plan.date]);
      end
  else
      if date < plan.date(1) || date > plan.date(end)
          error(['in flip_plan the fifth argument (date='  date ') must lay iside the plan.date ' plan.date]);
      end
  end
  if ~isempty(plan.shock_vars_)
      common_var = find(iy == plan.shock_vars_);
      if ~isempty(common_var)
          common_date = intersect(date, plan.shock_date_{common_var});
          if ~isempty(common_date)
              if common_date.length > 1
                  the_dates = [cell2mat(strings(common_date(1))) ':' cell2mat(strings(common_date(end)))];
              else
                  the_dates = cell2mat(strings(common_date));
              end
              error(['Impossible case: ' plan.exo_names{plan.shock_vars_(common_var)} ' is used both as a shock and as an endogenous variable to control the path of ' plan.endo_names{ix} ' at the dates ' the_dates]);
          end
      end
  end
  if isempty(plan.constrained_vars_)
      plan.constrained_vars_ = ix;
      plan.options_cond_fcst_.controlled_varexo  = iy;
      if strcmp(expectation_type, 'perfect_foresight')
          plan.constrained_perfect_foresight_ = 1;
      else
          plan.constrained_perfect_foresight_ = 0;
      end
  else
      plan.constrained_vars_ = [plan.constrained_vars_ ; ix];
      plan.options_cond_fcst_.controlled_varexo  = [plan.options_cond_fcst_.controlled_varexo ; iy];
      if strcmp(expectation_type, 'perfect_foresight')
          plan.constrained_perfect_foresight_ = [plan.constrained_perfect_foresight_ ; 1];
      else
          plan.constrained_perfect_foresight_ = [plan.constrained_perfect_foresight_ ; 0];
      end
  end
  plan.constrained_date_{length(plan.constrained_date_) + 1} = date;
  plan.constrained_paths_{length(plan.constrained_paths_) + 1} = value;
