function [R_sq]=R_squared(y,yf)  

% function [R_squared]=R_squared(y,yf)  
% ------------------------------------------------------------------------
% This function calculates the coefficient of determination (R-Squared) for
% the (e.g. measurement) data |y| and the data |yf| (e.g. a model fit). 
% NaN entries in either inputs are ignored. 
%
%
% Change log: 
% 2008/10/05
% 2019/06/26 Updated description
% 2019/06/26 Updated handling of NaN entries in the data
% ------------------------------------------------------------------------

%%

L=~isnan(y) & ~isnan(yf); %Logic for non-NaN entries

y_bar=mean(y(L)); %Mean of y
SS_err=sum((y(L)-yf(L)).^2); %Sum of differences Of y with yf
SS_tot=sum((y(L)-y_bar).^2); %Sum of differences of y with mean
R_sq=1-(SS_err./SS_tot); %R-squared value
 
%% 
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% License: <https://github.com/gibbonCode/GIBBON/blob/master/LICENSE>
% 
% GIBBON: The Geometry and Image-based Bioengineering add-On. A toolbox for
% image segmentation, image-based modeling, meshing, and finite element
% analysis.
% 
% Copyright (C) 2006-2022 Kevin Mattheus Moerman and the GIBBON contributors
% 
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