%%********************************************************
%% qops:  Fu = qops(pblk,w,f,options,u);
%% 
%% options = 1, Fu(i) = <wi,fi> 
%%         = 2, Fu(i) = 2*wi(1)*fi(1)-<wi,fi>
%%         = 3, Fui   = w(i)*fi
%%         = 4, Fui   = w(i)*fi, Fui(1) = -Fui(1). 
%% options = 5, Fu = w [ f'*u ; ub + fb*alp ], where 
%%              alp = (f'*u + u0)/(1+f0);  
%% options = 6, compute Finv*u. 
%%
%% Note F = w [f0  fb'; fb  I+ fb*fb'/(1+f0) ], where
%%      f0*f0 - fb*fb' = 1. 
%%      Finv = (1/w) [f0  -fb'; -fb  I+ fb*fb'/(1+f0) ].
%%*****************************************************************
%% SDPT3: version 4.0
%% Copyright (c) 1997 by
%% Kim-Chuan Toh, Michael J. Todd, Reha H. Tutuncu
%% Last Modified: 16 Sep 2004
%%*****************************************************************

   function  Fu = qops(pblk,w,f,options,u); 

   if (options >= 1 & options <= 4)
      Fu = mexqops(pblk{2},w,f,options); 
   elseif (options == 5)
      s = 1 + [0 cumsum(pblk{2})]; 
      idx1 = s(1:length(pblk{2})); 
      inprod = mexqops(pblk{2},f,u,1); 
      tmp = (u(idx1)+inprod)./(1+f(idx1)); 
      Fu  = u + mexqops(pblk{2},tmp,f,3); 
      Fu(idx1) = inprod; 
      Fu = mexqops(pblk{2},w,Fu,3); 
   elseif (options == 6)
      s = 1 + [0 cumsum(pblk{2})]; 
      idx1 = s(1:length(pblk{2})); 
      gamprod = mexqops(pblk{2},f,u,2);
      tmp = (u(idx1)+gamprod)./(1+f(idx1)); 
      Fu  = u - mexqops(pblk{2},tmp,f,3); 
      Fu(idx1) = gamprod;
      Fu = mexqops(pblk{2},1./w,Fu,3); 
   end
%%********************************************************