How can I fit a curve to x, y points and obtain the regression?

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Sarah 2018-11-19

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评论： Sarah 2018-11-20

I have plotted x vs y and obtained a plot of points, now I'm trying to fit a curve to my data using a nonlinear polynomial of order 4, the coeficiants are unknown.

I aim to obtain the regression coefficient as well.

Any idea how it is possible to do this? what are the suitable matlab functions to plot the fitting curve and to obtain the regression coeficient?

I already tried polyfit, but is it correct? if yes then how to proceed?

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回答（3 个）

KSSV 2018-11-19

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编辑：KSSV 2018-11-19

在 MATLAB Online 中打开

Yes polyfit is the function you need.

x = linspace(0,4*pi,50);
y = sin(x);
% Use polyfit to fit a 4th-degree polynomial to the points.
p = polyfit(x,y,7);
% Evaluate the polynomial on a finer grid and plot the results.
x1 = linspace(0,4*pi);
y1 = polyval(p,x1);
figure
plot(x,y,'o')
hold on
plot(x1,y1)
hold off

In the above p has your coefficients. YOu can use poly2sym to see the polynomial obtained.

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KSSV 2018-11-20

Then using polyfit is apt.

Sarah 2018-11-20

so i tried this as below, but the resulting fitting does not apear same as it is when done on excel.

x =[6 values input by the user ]

y = [6 values calculated ]

so x and y are the same size

then:

p = polyfit(x, y, 4);

val = polyval(p, x);

plot(x, y, 'o');

hold on;

plot(x, val);

hold off

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madhan ravi 2018-11-19

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在 MATLAB Online 中打开

Read interp1 and use appropriate method you want

x = linspace(0,4*pi,50);
y = sin(x);
xx = linspace(x(1),x(end),1000);
yy = interp1(x,y,xx,'spline')
plot(x,y,'o',xx,yy)

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madhan ravi 2018-11-19

Anytime :) , polyfit is for polynomials

Sarah 2018-11-19

then how can i get the regression coeficient if I am sing the interp1 method?

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Luna 2018-11-19

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编辑：Luna 2018-11-19

Hello Sarah,

you can use polyfit. It uses least squares, here is the link you can read about it:

polyfit