cs_cosamp.m

function hat_x=cs_cosamp(y,T_Mat,m)


n=length(y);                           % length of measurements
s=floor(n/4);                                 % sparsity                  
r_n=y;                                 % initial residuals

sig_pos_lt=[];                         % significant pos for last time iteration

for times=1:s                          % number of iterations

    product=abs(T_Mat'*r_n);
    [val,pos]=sort(product,'descend');
    sig_pos_cr=pos(1:2*s);             % significant pos for current iteration

    sig_pos=union(sig_pos_cr,sig_pos_lt);

    Aug_t=T_Mat(:,sig_pos);            % current selected entries of T_Mat 

    aug_x_cr=zeros(m,1);               
    aug_x_cr(sig_pos)=(Aug_t'*Aug_t)^(-1)*Aug_t'*y;  % temp recovered x (sparse)

    [val,pos]=sort(abs(aug_x_cr),'descend');

    hat_x=zeros(1,m);
    hat_x(pos(1:s))=aug_x_cr(pos(1:s));% recovered x with s sparsity  

    sig_pos_lt=pos(1:s);               % refresh the significant positions

    r_n=y-T_Mat*hat_x';
end