So when using polyfit I get a really nice line ploted and matches my data well. Unfortunately when I go to use the coefficients determined by polyfit, it doesn't make sense at all! My expected slope c(1) is around 0.3 but I'm getting around 6. Even when I do the approximate calculation of the slope by hand it is as expected so my data mustn't be wrong.
Here's my code...
N=10:10:60;
t1 = [3.5 6.5 10 12.5 15.5 19];
t2 = [3 6.5 10 13 16 20];
t3 = [3 7 10.5 13.5 17 20];
t4 = [4 7 10 13 16.5 20];
t5 = [3.5 7 11 14.5 18 20.5];
T = [t1;t2;t3;t4;t5];
m = mean(T);
[c,S,mu] = polyfit(N,m,1);
ci = polyparci(c,S);
disp(['Equation is y = ' num2str(c(1)) '*x + ' num2str(c(2))])
disp(['Wavelength is ' num2str(2.*c(1)) ' micrometers'])
[y_est, delta] = polyval(c,N,S,mu);
f = c(1)*N + c(2);
hold on
scatter(N,m,'b')
plot(N,y_est,'r')
plot(N,f,'g')
hold off
I've added a plot of the function of the function with the coefficients
f = c(1)*N + c(2);
plot(N,f,'g')
to show how they are incorrect. This is the plot it outputs.
I thought I used polyfit correctly but I must not have. Where have I gone wrong?
