What code do I use to add a regression (least squares) line to an existing scatter graph?

I have created scatter graphs in Matlab using the plot(x,y) function, but how do I now add regression lines to them?

Answer 1

[Star Strider]

You can use polyfit and polyval (or a number of other regression options if you have the Statistics Toolbox), and using variations on this simple two-parameter linear regression:

B = [ones(size(x(:))  x(:)]\y(:);
y_fit = [ones(size(x(:))  x(:)]*B;

Here ‘B’ are the estimated parameters and ‘y_fit’ is the fitted regression line. To plot them (assuming your variables are sorted with ‘x’ as either ascending or descending)

figure(1)
scatter(x, y)
hold on
plot(x, y_fit)
hold off
grid

Answer 2

[Image Analyst]

See my attached demo on polyfit below this image it creates.

Feel free to adapt as needed.