% Illustration of linear least squares. function main()        % KSmrq's colors    red    = [0.867 0.06 0.14];    blue   = [0, 129, 205]/256;    green  = [0, 200,  70]/256;    yellow = [254, 194,   0]/256;    white = 0.99*[1, 1, 1];    gray = 0.2*white;     % Set up the grid and other parameters    N = 100;    A = -2.2; B = 2;     X = linspace(A, B, N);    C=-4; D = 4;        % Set up the figure    lw = 4; % linewidth    fs = 18; % font size    figure(1); clf; hold on;    set(gca, 'fontsize', fs);    set(gca, 'linewidth', lw/2.5)    hold on; grid on;     % random numbers    a = 1.1; b = 3.5; c = 1.4;    M = 50;    XX=linspace(A+0.3, B-0.3, M+1);    Xr = 0*(1:M);    Yr = Xr;    for i=1:M       r=rand(1);       Xr(i) = XX(i)*r+XX(i+1)*(1-r);       Yr(i) = a*Xr(i) + b + c*0.4*erfinv(2*rand(1) - 1);    end     myrad = 0.05;    for i=1:length(Xr)       ball(Xr(i), Yr(i), myrad, red);    end      % least squares fitting    Yr = Yr';    Mat = [Xr' (0*Xr+1)'];    V=Mat'*Yr;    V=(Mat'*Mat)\V;    ae = V(1); be = V(2);       plot(X, ae*X+be, 'b', 'linewidth', lw);     grid on;    set(gca, 'GridLineStyle', '-', 'xcolor', gray);    set(gca, 'GridLineStyle', '-', 'ycolor', gray);    set(gca, 'XTick', [-2 -1 0 1 2]);      axis equal;    axis([-2, 2, 1, 6]);        saveas(gcf, 'Linear_least_squares.eps', 'psc2'); % save as eps    %plot2svg('Linear_least_squares.svg'); % save as svg      function ball(x, y, r, color)    Theta=0:0.1:2*pi;    X=r*cos(Theta)+x;    Y=r*sin(Theta)+y;    H=fill(X, Y, color);    set(H, 'EdgeColor', 'none');