From a5e60834caa6822e5f2d97949b8cd7c0e0953a7f Mon Sep 17 00:00:00 2001
From: Johannes Pfeifer <jpfeifer@gmx,de>
Date: Sat, 13 Sep 2014 11:10:14 +0200
Subject: [PATCH] Ascertain that only correct steady states for linear models
 are accepted

Without the check, incorrect steady states were accepted. This happened for example if the model was not linear in the first place and solving a wrongly presumed linear equation system did not work.
---
 matlab/evaluate_steady_state.m | 11 +++++++++--
 matlab/print_info.m            | 12 +++++++++---
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/matlab/evaluate_steady_state.m b/matlab/evaluate_steady_state.m
index 208f665bf..37808c4a1 100644
--- a/matlab/evaluate_steady_state.m
+++ b/matlab/evaluate_steady_state.m
@@ -207,9 +207,16 @@ function [ys,params,info] = evaluate_steady_state(ys_init,M,options,oo,steadysta
                 disp(['STEADY:  numerical initial values or parameters incompatible with the following' ...
                       ' equations'])
                 disp(ii')
-                disp('Check whether your model in truly linear')
+                disp('Check whether your model is truly linear. Put "resid(1);" before "steady;" to see the problematic equations.\n')
             elseif isempty(ii) && max(abs(fvec)) > 1e-12
                 ys = ys_init-jacob\fvec;
+                resid = evaluate_static_model(ys,exo_ss,params,M,options);
+                if max(abs(resid)) > 1e-6
+                    check=1;
+                    fprintf('STEADY: No steady state for your model could be found\n')
+                    fprintf('STEADY: Check whether your model is truly linear. Put "resid(1);" before "steady;" to see the problematic equations.\n')
+                end
+
             else
                 ys = ys_init;
             end
@@ -225,7 +232,7 @@ function [ys,params,info] = evaluate_steady_state(ys_init,M,options,oo,steadysta
                             fprintf('STEADY:  Derivative of Equation %d with respect to Variable %s  (initial value of %s: %g) \n',infrow(ii),deblank(M.endo_names(orig_var_index,:)),deblank(M.endo_names(orig_var_index,:)),ys_init(infcol(ii)))
                         end
                     end
-                    disp('STEADY: Check whether your model in truly linear\n')
+                    fprintf('Check whether your model is truly linear. Put "resid(1);" before "steady;" to see the problematic equations.\n')
                 end
             end
         end
diff --git a/matlab/print_info.m b/matlab/print_info.m
index 91c2100c0..795ecbd2d 100644
--- a/matlab/print_info.m
+++ b/matlab/print_info.m
@@ -75,9 +75,15 @@ if ~noprint
       case 19
         error('The steadystate file did not compute the steady state')
       case 20
-        error(['Impossible to find the steady state. Either the model' ...
-               ' doesn''t have a steady state, there are an infinity of steady states, ' ...
-               ' or the guess values are too far from the solution'])
+        if DynareOptions.linear
+            error(['Impossible to find the steady state. Either the model' ...
+                   ' doesn''t have a steady state or there are an infinity of steady states.' ...
+                   ' Check whether your model is truly linear or whether there is a mistake in linearization.'])        
+        else
+            error(['Impossible to find the steady state. Either the model' ...
+                   ' doesn''t have a steady state, there are an infinity of steady states,' ...
+                   ' or the guess values are too far from the solution'])
+        end
       case 21
         error('The steady state is complex')
       case 22