How to obtain r^2 (r squared) value of linear regression plotted using 'lsline'
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Hello, what is the syntax to obtain the r-squared (r^2) value if I plotted a best fit linear regression with the 'lsline' function?
2 Comments
Scott MacKenzie
on 21 Mar 2022
You can't get r^2 from lsline. lsline is created from the points. To get r^2, you also need to work with the points. Use the corrcoef function to get r (and then r^2) from the points.
Answers (1)
Mathieu NOE
on 22 Mar 2022
hello
see suggestion below - even no need of lsline
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/936674/image.png)
clc
clearvars
% dummy data
x = (0:100);
a = 1.5;
b = 0.235;
y = a*x +b + 3*randn(size(x));
% Fit a polynomial p of degree "degree" to the (x,y) data:
degree = 1;
p = polyfit(x,y,degree);
% Evaluate the fitted polynomial p and plot:
f = polyval(p,x);
eqn = poly_equation(flip(p)); % polynomial equation (string)
Rsquared = my_Rsquared_coeff(y,f); % correlation coefficient
figure(1);plot(x,y,'*',x,f,'-')
legend('data',eqn)
title(['Data fit , R² = ' num2str(Rsquared)]);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function Rsquared = my_Rsquared_coeff(data,data_fit)
% R2 correlation coefficient computation
% The total sum of squares
sum_of_squares = sum((data-mean(data)).^2);
% The sum of squares of residuals, also called the residual sum of squares:
sum_of_squares_of_residuals = sum((data-data_fit).^2);
% definition of the coefficient of correlation is
Rsquared = 1 - sum_of_squares_of_residuals/sum_of_squares;
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function eqn = poly_equation(a_hat)
eqn = " y = "+a_hat(1);
for i = 2:(length(a_hat))
if sign(a_hat(i))>0
str = " + ";
else
str = " ";
end
if i == 2
% eqn = eqn+" + "+a_hat(i)+"*x";
eqn = eqn+str+a_hat(i)+"*x";
else
% eqn = eqn+" + "+a_hat(i)+"*x^"+(i-1)+" ";
eqn = eqn+str+a_hat(i)+"*x^"+(i-1)+" ";
end
end
eqn = eqn+" ";
end
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