function  [coef, RSquared]=plotfit(x,y,polyorder)
% plotfit(,y,polyorder) plots x,y data in the vectors "x" 
% and "y", fits it to a polynomial of order "polyorder", 
% plots the data and the fit, and displays the fit 
% coefficients and the goodness-of-fit measure R-squared
% in the upper left corner of the graph.
% polyorder=1 for straight line, =2 for quadratic (parabola) etc.
% Tom O'Haver, 2008

coef=polyfit(x,y,polyorder);
% Plot the data and the polynomial fit
xx=linspace(min(x),max(x));
yhat=polyval(coef,xx);
plot(x,y,'.r',xx,yhat,'-g')
axis([min(x) max(x) min(y) max(y)]);
xlabel('x');ylabel('y')

% Compute the correlation coefficient and R-Squared
cc=corrcoef(polyval(coef,x),y);
RSquared=cc(2).^2;

% Label the graph with the fit information
text(min(x),max(y)-.05.*(max(y)-min(y)),['   Polynomial Order of fit = ' num2str(polyorder)] );
text(min(x),max(y)-.1.*(max(y)-min(y)),['   Fit coefficients = ' num2str(coef)] );
text(min(x),max(y)-.15.*(max(y)-min(y)),['   R-Squared = ' num2str(RSquared)] );