MATLAB: Polyfit is not showing the expected fit

Question

Hi, I'm trying to fit a collection of data points to a line, but when I call polyfit, it returns a completely unexpected result for both the slope and the y-intercept. I checked the help section and documentation but I don't know what I'm doing wrong…

I even tried finding the fit for a line, and it failed too. This is the code I'm using:

t = linspace(0,2); 
x = 2*t+3;
[p,S,mu] = polyfit(t,x,1);
polyval(p,t,S);
plot(t,x)
hold on
[y,delta] = polyval(p,t,S);
errorbar(t,y,delta)
legend('line','fit')

And this is the plot I get:

Please let me know if I'm doing anything incorrectly.

Thanks in advance.

Answer 1

You forgot to include ‘mu’ in your polyval argument list. If you ask for it in polyfit, you need to include it in polyval:

[y,delta] = polyval(p,t,S,mu);