trap the case when Q is singular

matlab/compute_Pinf_Pstar.m

@@ -48,6 +48,12 @@ function [Pstar,Pinf] = compute_Pinf_Pstar(mf,T,R,Q,qz_criterium, restrict_colum
 % along with Dynare.  If not, see <https://www.gnu.org/licenses/>.
 
 np = size(T,1);
+if not(any(any(Q)))
+    Pstar=T*0;
+    Pinf=T*0;
+    return
+end
+
 if nargin == 6
     indx = restrict_columns;
     indx0=find(~ismember([1:np],indx));