How to plot a 3rd order best fit line through 3 sets of data?

I have 3 sets of data as vectors. X terms Cp80, Cp50, Cp30 and their corresponding Cv80, Cv50, and Cv30 y terms. I currently am using this block of code to plot them.

figure
hold on
plot(Cv80,Cp80,'*')
plot(Cv50,Cp50,'o')
plot(Cv30,Cp30,'p')
hold off

I need to run a third order best fit line through these three data sets and generate the R^2 value. I am unfamiliar with Polyfit, as I always use the basic fitting tools on the plot, and the documentation is less than helpful. I would appreciate it greatly if someone could show me how to fit one line and its R^2 value to these three datasets.

Answer 1

[Roger Stafford]

How about

x1 = [Cv80(:);Cv50(:);Cv30(:)];
y1 = [Cp80(:);Cp50(:);Cp30(:)];
p = polyfit(x1,y1,3);
y = polyval(p,x1);
plot(x1,y)

If the values of x1 are not monotone, you can first sort them:

x1 = [Cv80(:);Cv50(:);Cv30(:)];
y1 = [Cp80(:);Cp50(:);Cp30(:)];
[x1,ix] = sort(x1);
y1 = y1(ix);
p = polyfit(x1,y1,3);
y = polyval(p,x1);
plot(x1,y)

Answer 2

[Muhammad Usman Saleem]

for R^2