function [xdsube,Brow,Erow] = fn_dataext2(Byrqm,Eyrqm,xdatae)
% xdsube = dataext(Byrqm,Eyrqm,xdatae)
%      Extract subset of xdatae, given Byrqm and Eyrqm
%
% Byrqm: [year quarter(month)]: beginning year and period.  If Byqm(2)=0, we get annual data.
% Eyrqm: [year period]:  end year and period.  If Byrqm(2)=0, it must be Eyrqm(2)=0.
% xdatae:  all data (some of which may be NaN) with the first 2 columns indicating years and periods.
%----------
% xdsube:  subset of xdatae.
% Brow:  the row number in xdatee that marks the first row of xdsube.
% Erow:  the row number in xdatee that marks the last row of xdsube.
%
% Tao Zha, April 2000

if (Byrqm(2)==0)
    Eyrqm(2)=0;
    q_m1=find(xdatae(:,2)==xdatae(1,2));   % Locating quarter or month
    if length(q_m1)<2
      error('The matrix xdatae must at least have a cycle of q_m periods for possibly one calendar year')
    end
    q_m=q_m1(2)-1;
end

Brow = min(find(xdatae(:,1)==Byrqm(1)));
if isempty(Brow)
   error('Byrqm is outside the date range indicated by xdatae(:,1:2)!')
end
if Byrqm(2)>0
   nadt=Byrqm(2)-xdatae(Brow,2);
   if nadt<0
      error('Byrqm is outside the date range indicated by xdatae(:,1:2)!')
   end
   Brow=Brow+nadt;
end
%
Erow = min(find(xdatae(:,1)==Eyrqm(1)));
if isempty(Erow)
   error('Eyrqm is outside the date range indicated by xdatae(:,1:2)!')
end
if Eyrqm(2)>0
   nadt2=Eyrqm(2)-xdatae(Erow,2);
   if nadt<0
      error('Eyrqm is outside the date range indicated by xdatae(:,1:2)!')
   end
   Erow=Erow+nadt2;
end
%

if (Byrqm(2)==0)     % By calendar years.
   if (xdatae(Brow,2)~=1) | (xdatae(Erow,2)~=1)
      error('Calendar years extracted here must have q_m periods')
   end
   Erow=Erow+q_m-1;
end

xdsube = xdatae(Brow:Erow,:);   % with dates