Why does polyfit gives two outputs?

Hi,

I want to plot a line passing through a set of points, which is as in the code below.

To determine the slope I used polyfit.

But it gives two outputs.

I wonder which output I should consider out of the two outputs it is giving me?

clc;
clear;
phi_1 = [0.1724*pi  0.1472*pi  2.18*pi  2.25*pi  4*pi  3.588*pi  1.012*pi  4.112*pi  4.31*pi  4.25*pi  0.832*pi];
x1 = linspace(0,1,11);
figure(1)
plot(x1,phi_1,'o');

coefficients1=polyfit(x1,phi_1,1)

coefficients1 = 1×2

7.6641 3.8373

slope1=coefficients1(1);

With regards,

rc

Answer 1

[Matt J]

It doesn't give 2 outputs unless you call it with 2 output arguments. The one output that it is giving you is a vector with 2 coefficients (a slope and an intercept) because that's what a first order polynomial has.

Answer 2

[the cyclist]

The first line of the function description on the documentation for polyfit states precisely what those outputs are.

They are the coefficients of the descending powers of the fitted polynomial. You asked for a 1st-order polynomial, so the first element of the output is the coefficient of the linear (1st-order) term, and the second element of the output is the coefficient of the intercept (the 0th-order term).

clc;
clear;
phi_1 = [0.1724*pi  0.1472*pi  2.18*pi  2.25*pi  4*pi  3.588*pi  1.012*pi  4.112*pi  4.31*pi  4.25*pi  0.832*pi];
x1 = linspace(0,1,11);

coefficients1=polyfit(x1,phi_1,1)

coefficients1 = 1×2

7.6641 3.8373

slope1=coefficients1(1);
intercept1=coefficients1(2)

intercept1 = 3.8373

figure(1)
hold on
plot(x1,phi_1,'o');
plot([0 1],intercept1 + slope1*[0 1])

[Rahul]

Hi Matt & the cyclist,

Thanks a lot for your reply.It indeed helped me.

I also wish to convert x1 from linear scale to angular scale (in radians)

I can see in the documentation, probably dist is a function which can be used but I'm not sure how to implement the parameters quatA and quatB.

kindly advice.

Sincerely,

rc

[the cyclist]

Assuming that you are not working with quaternions, I doubt that dist is the function you need.

Please give more detail about what you are trying to do. (You might actually want to open a new question, since your original one has been answered.)