% 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.
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]);
error(['impossible case you have two conditional forecasts:\n - one involving 'plan.endo_names{plan.options_cond_fcst_.controlled_varexo(i_ix),:}' as control and 'plan_exo_names{plan.constrained_vars_(ix_)}' as constrined endogenous\n - the other involving 'plan.endo_names{plan.options_cond_fcst_.controlled_varexo(iy),:}' as control and 'plan_exo_names{plan.constrained_vars_(ix)}' as constrined endogenous\n']);