 function    Kd=Fpmulow(Lam,X,lowinds,V,H)
%   find the variable (bottom) part of operator F'mu
V=sparse(V);
H=sparse(H);
X=sparse(X);
Lam=sparse(Lam);
n1=size(X,1);
%  block column one
En=speye(n1);
Kd=sparse([sparse(kron(En,Lam))*sparse(lowinds) ...
            sparse(kron(X,En))*sparse(lowinds)]);
