How can I fit a scatter plot?

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?

[Adam Danz]

Is your goal to fit all the data together or to fit each of the 7 groups individually?

Answer 1

[Adam Danz]

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))

Answer 2

[Anton Kogios]

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.