How to find a polynomial that best fit with scatter plot?
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Hi everyone,
I am trying to find a best-fit polynomial equation that works well for my data set (two parameters x, and y).
First, I attempt to fit a polynomial line using Excel (figure attached). The equation shows the best fit with the original scatter plot (the red line is the best fit polynomial line).
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1381034/image.png)
However, when I try to estimate values with the best-fit equation, it looks very different from actual data points.
A similar error is observed when I attempt to use the Matlab function polyfilt.
clear all
clc
data=readmatrix('lv_vl.csv');
x=data(:,1);
y=data(:,2);
scatter(x,y,'b')
p = polyfit(x,y,2)
May someone suggets me how i can fix this.
(data is also attached).
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Accepted Answer
Walter Roberson
on 12 May 2023
Edited: Walter Roberson
on 12 May 2023
data=readmatrix('lv_vl.csv');
x=data(:,1);
y=data(:,2);
scatter(x,y,5,'.r')
p = polyfit(x,y,2);
eqn = poly2sym(p)
xest = linspace(min(x), max(x), 75);
yest = polyval(p, xest);
hold on
plot(xest, yest, '-b');
title(char(vpa(eqn,5)))
9 Comments
Walter Roberson
on 14 May 2023
The sum of squared error is still pretty high for degree 4, and there are still fairly visible artifacts.
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