D = [ 3.85 3.80 5.50 7.38 3.75 4.00 6.75 8.51 3.70 4.30 7.25 9.52 3.70 3.70 5.50 7.50 3.60 3.85 7.00 9.33 3.60 3.80 6.50 8.28 3.60 3.75 6.75 8.75 3.80 3.85 5.25 7.87 3.80 3.65 5.25 7.10 3.85 4.00 6.00 8.00 3.90 4.10 6.50 7.89 3.90 4.00 6.25 8.15 3.70 4.10 7.00 9.10 3.75 4.20 6.90 8.86 3.75 4.10 6.80 8.90 3.80 4.10 6.80 8.87 3.70 4.20 7.10 9.26 3.80 4.30 7.00 9.00 3.70 4.10 6.80 8.75 3.80 3.75 6.50 7.95 3.80 3.75 6.25 7.65 3.75 3.65 6.00 7.27 3.70 3.90 6.50 8.00 3.55 3.65 7.00 8.50 3.60 4.10 6.80 8.75 3.65 4.25 6.80 9.21 3.70 3.65 6.50 8.27 3.75 3.75 5.75 7.67 3.80 3.85 5.80 7.93 3.70 4.25 6.80 9.26 ]; y = D(:,4); x1 = D(:,2)-D(:,1); x2 = D(:,3); n = size(D,1); %--------- close; figure('Position',[100 100 900 400]); subplot(1,2,1); hold on; plot(x1,y,'ro','markersize',10,'markerface','c'); p1 = polyfit(x1,y,1); xx1 = linspace(-0.2,0.6,100); yy1 = polyval(p1,xx1); plot(xx1,yy1,'r-','linewidth',3); xlabel('x_1','fontsize',18); ylabel('y','fontsize',18); %--------- subplot(1,2,2); hold on; plot(x2,y,'bo','markersize',10,'markerface','y'); p2 = polyfit(x2,y,2); xx2 = linspace(5,7.5,100); yy2 = polyval(p2,xx2); plot(xx2,yy2,'b-','linewidth',3); xlabel('x_2','fontsize',18); ylabel('y','fontsize',18); %--------- alpha = 0.05; x = [ ones(n,1) x1 x2 x2.^2]; [b,bint,r,rint,stats] = regress(y,x,alpha)