calculate slope from linear fit data

I have this code to linear fit data

    x = 1:10; 
    y1 = [1 5 7 8 9 15 16 12 18 20]; 
    scatter(x,y1,'b','*') 
    P = polyfit(x,y1,1);

      slope = P(1)
      intercept = P(2)

      yfit = P(1)*x+P(2);  % P(1) is the slope and P(2) is the intercept
      hold on;
      plot(x,yfit,'r-.')
And the figure I got from code is attached here

The intercept from figure should be 2.2. But I get the value from code is 0.5.

I didn't understand why the values are different? The code seems correct to me. Any suggestion from anyone?

Answer 1

[Ameer Hamza]

The intercept is indeed 0.5. Intercept is the value on y-axis when x=0. Whereas you 2.2 is the value when x=1.

Answer 2

[Edward Vivanco]

Error in 1st line: x = 1:10

Fix: x = 0:10