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calculate slope from linear fit data

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Namira
Namira on 11 Aug 2018
Answered: Edward Vivanco on 10 Nov 2019
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?

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Accepted Answer

Ameer Hamza
Ameer Hamza on 11 Aug 2018
Edited: Ameer Hamza on 11 Aug 2018
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.

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More Answers (1)

Edward Vivanco
Edward Vivanco on 10 Nov 2019
Error in 1st line: x = 1:10
Fix: x = 0:10

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