Plot sigma value to linear curve

Hi all. I am trying to figure out how to plot the sigma value to the linear curve. I have my code down below and a figure of what I want to do.

% 
td=[-1 0 1 2 3 4 6 7]';
yd=[-0.75 0.3 3 4 5.6 7 6.4 8.4]';
A=[ones(size(td)) td];
x=A\yd; a=x(1); b=x(2);
n=length(td);
e=norm(A*x-yd)/sqrt(n)
y=a+(b*td);
plot(td,y,); hold on

My code now plots the linear curve and calculates all values that I need, and the final thing I need is to plot the green lines that are sort of "errors". The image I got is a screenshot of what I want to achieve.

Thanks, Joakim

Answer 1

[SRT HellKitty]

To get a vertical line you use the a simple 2 element vector where x does not change(to make a horizontal line simply make the y constant) such as;

 plot([xConstant, xConstant], [yStart, yEnd])

So for that first green line in the image above that goes from (-1, -1) to (-1,0) it would look like this;

plot([-1, -1], [-1 0])

now to add this into a for loop you could do the following, which will create the lines you request;

for ii = 1:length(td)
  plot([td(ii), td(ii)], [yd(ii), y(ii)])
end