How to find the Linear Regression?

Hi

I fitted the data using the fminsearch. I am able to find the slope and intercept of the fitted equation but, how to find the Linear Regression (R2) value of the fitted equation?

code:

for i=1:3
    y=[Y1{i,1}']
    x=[X{i,1}']

                A= fminsearch(@(par_fit) funccoats(par_fit,x,y),rand(1,2));
                B(i,1)=A(:,1)
                C(i,1)=A(:,2)
     end

graph: