# Given a set of date point x and y, estimate three polynomial functions (2nd degree, 3rd degree, 4th degree) that will best fit the data.

5 views (last 30 days)
John Doe on 27 Nov 2021
Commented: Walter Roberson on 27 Nov 2021
Given a set of date point x and y, estimate three polynomial functions (2nd degree, 3rd degree, 4th degree) that will best fit the data. Compute new set of y data from the three functions and determine which of the three functions will give the least norm difference.
This is what I've came up with, but still not sure if it really satisfy the problem.
x=[0.9 1.5 3 4 6 8 9.5];
y=[0.9 1.5 2.5 5.1 4.5 4.9 6.3];
p=polyfit(x,y,3)
xp=0.9:0.1:9.5;
yp=polyval(p,xp);
plot(x,y,'o',xp,yp)
xlabel('x'); ylabel('y')

Walter Roberson on 27 Nov 2021
The question is expecting you to also polyfit with degree 2 and 4, and to polyval with those, and to compute the norm() of the projected values against the actual values, and then to see whether degree 2, degree 3, or degree 4 gave the best fit.
##### 2 CommentsShowHide 1 older comment
Walter Roberson on 27 Nov 2021
x = [0.9 1.5 3 4 6 8 9.5];
y = [0.9 1.5 2.5 5.1 4.5 4.9 6.3];
p = polyfit(x,y,2);
l = polyfit(x,y,3);
t = polyfit(x,y,4);
xp = 0.9:0.1:9.5;
yp1 = polyval(p,xp);
yp2 = polyval(l,xp);
yp3 = polyval(t,xp);
xlabel('x');
ylabel('y');
plot(x,y,'o',xp,yp1,xp,yp2,xp,yp3)

### Categories

Find more on Polynomials in Help Center and File Exchange

R2019a

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by