function [RSq] = RSquared(ymodel, ydata)
%Calculate the coefficient of determination (R^2) between a set of real and
%modelled vaues

%Arguments:
%IN:
%ymodel - array of corresponding modelled values.
%ydata - array of real data values of the dependant variable

%OUT:
%RSq - calculated coefficient of determination


%Load chain age data

ChainAges = load('-NAME OF FILE-') ;
xdata = (ChainAges(: ,1)) ;
ydata = (ChainAges(: ,2)) ;


PC = polyfit(xdata, ydata, 1) ;
Gradient = PC(1) ;
Intercept = PC(2) ;

%

s = 0 ;

for a = 1:length(ydata)
    s = s + ydata(a);
end
ymean = s/length(ydata) ;

%

ymodel = (Gradient*xdata) + Intercept ;

for b = 1:length(ydata)
    SSerrArray(b) = ((ymodel(b) - ydata(b))^2) ;
end

SSerrArray1 = SSerrArray(b) ;
SSerr = 0 ;

for b = 1:length(ydata)
    SSerr = SSerr + SSerrArray1 ;
end

%

for c = 1:length(ydata)
    SStotArray(c) = ((ydata(c) - ymean)^2) ;
end

SStotArray1 = SStotArray(c) ;
SStot = 0 ;

for d = 1:length(ydata)
    SStot = SStot + SStotArray1 ;
end

%

RSq = 1 - (SSerr/SStot) ;

display(RSq)