Пошагово объясните код recpo_ls (очень много вопросов)

function [pos, El, GDOP, basic_obs] = recpo_ls(obs,sats,time,Eph) 
% RECPO_LS Computation of receiver position from pseudoranges 
%          using ordinary least-squares principle 
 
%Kai Borre 31-10-2001 
%Copyright (c) by Kai Borre 
%$Revision: 1.1 $  $Date: 2002/07/10  $ 
 
v_light = 299792458; 
dtr = pi/180; 
m = size(obs,1);  % number of svs 
el = zeros(m,1); 
% identify ephemerides columns in Eph 
for t = 1:m 
    col_Eph(t) = find_eph(Eph,sats(t),time); 
end 
% preliminary guess for receiver position and receiver clock offset 
pos = zeros(4,1); 
no_iterations = 6;  
ps_corr = []; 
sat_pos = []; 
 
for iter = 1:no_iterations 
    A = []; 
    omc = []; % observed minus computed observation 
    W = []; %weighted least square 
    for i = 1:m         
        k = col_Eph(i); 
        tx_RAW = time - obs(i)/v_light; 
        t0c = Eph(21,k); 
        dt = check_t(tx_RAW-t0c); 
        tcorr = (Eph(2,k)*dt + Eph(20,k))*dt + Eph(19,k); 
        tx_GPS = tx_RAW-tcorr; 
        dt = check_t(tx_GPS-t0c); 
        tcorr = (Eph(2,k)*dt + Eph(20,k))*dt + Eph(19,k); 
        tx_GPS = tx_RAW-tcorr; 
        X = satpos(tx_GPS, Eph(:,k)); 
        if iter == 1 
            traveltime = 0.072; 
            Rot_X = X; 
            trop = 0; 
        else 
            rho2 = (X(1)-pos(1))^2+(X(2)-pos(2))^2+(X(3)-pos(3))^2; 
            traveltime = sqrt(rho2)/v_light; 
            Rot_X = e_r_corr(traveltime,X); 
            rho2 = (Rot_X(1)-pos(1))^2+(Rot_X(2)-pos(2))^2+(Rot_X(3)-pos(3))^2;           
            [az,el,dist] = topocent(pos(1:3,: ),Rot_X-pos(1:3,: ));                                                             
            if iter == no_iterations, El(i) = el; end 
            trop = tropo(sin(el*dtr),0.0,1013.0,293.0,50.0,... 
                0.0,0.0,0.0);     
        end 
        % subtraction of pos(4) corrects for receiver clock offset and 
        % v_light*tcorr is the satellite clock offset 
        if iter == no_iterations 
            ps_corr = [ps_corr; obs(i)+v_light*tcorr-trop]; 
            sat_pos = [sat_pos; X']; 
        end 
        omc = [omc; obs(i)-norm(Rot_X-pos(1:3),'fro')-pos(4)+v_light*tcorr-trop]; 
        A = [A; (-(Rot_X(1)-pos(1)))/obs(i)... 
                (-(Rot_X(2)-pos(2)))/obs(i) ... 
                (-(Rot_X(3)-pos(3)))/obs(i) 1]; 
    end % i 
    x = A\omc;
    pos = pos + x; 
    if iter == no_iterations, GDOP = sqrt(trace(inv(A'*A)));  
        %% two lines that solve an exercise on computing tdop 
        % invm = inv(A'*A); 
        % tdop = sqrt(invm(4,4)) 
    end 
end % iter 
basic_obs = [sat_pos ps_corr]; 
 
%%%%%%%%%%%%%%%%%%%%%  recpo_ls.m  %%%%%%%%%%%%%%%%%%%%%