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How can I fit a scatter plot?

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Giada
Giada on 23 Mar 2023
Answered: Adam Danz on 23 Mar 2023
In MATLAB, I created a scatter plot of my data with this code:
Lac = readmatrix("Lac.xlsx", "Range", "B2:Y8");
t = readmatrix("Lac.xlsx", "Range", "A2:A8");
scatter(t, Lac)
t is a 7x1 matrix; Lac is a 7x24 matrix.
How can I fit a line to this scatter plot?
  1 Comment
Adam Danz
Adam Danz on 23 Mar 2023
Is your goal to fit all the data together or to fit each of the 7 groups individually?

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Accepted Answer

Adam Danz
Adam Danz on 23 Mar 2023
This demo shows how to plot a linera fit using the entire data.
Fitting is demonstrated using fit (Curve Fitting Toolbox) and with polyfit.
t = rand(7,1)*10;
Lac = rand(7,24)+linspace(0,2,7)';
scatter(t,Lac,'bo')
tm = repelem(t,1,size(Lac,2));
If you have the Curve Fitting Toolbox: fit()
mdl = fit(tm(:),Lac(:),'Poly1')
mdl =
Linear model Poly1: mdl(x) = p1*x + p2 Coefficients (with 95% confidence bounds): p1 = -0.1431 (-0.1796, -0.1065) p2 = 2.209 (2.005, 2.413)
hold on
plot(mdl, 'r--')
Without the Curve Fitting Toolbox: polyfit()
coefs = polyfit(tm,Lac,1)
coefs = 1×2
-0.1431 2.2089
hold on
refline(coefs(1),coefs(2))

More Answers (1)

Anton Kogios
Anton Kogios on 23 Mar 2023
If you want to fit a line to the data as a whole, I think this should work:
t = 1:7;
Lac = randi(10,[7,24]);
scatter(t,Lac)
[coeffs] = polyfit(t,mean(Lac'),1)
hold on
plot(t,coeffs(1)*t+coeffs(2))
hold off
where the last argument for polyfit is the degree of the fit that you want.

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