How to code a basic fitting quadratic in this?

Hi everyone,

I am using two scatter plots. How can I code the quadratic fitting in that? I tried more than 7 ways on the internet and it's not working. It does not work with polyfit n=5. It just turns into a mesy multiple lines!

Thanks

s
ScatterPlotPreCOVID = scatter(x,y,'o')
hold on
ScatterPlotPostCOVID = scatter(x1,y1,'^')
hold off

Now, I do not insist coding it into it but I cannot have both quadratics simultanously for two datasets from the tools too.

Answer 1

[Walter Roberson]

P = polyfit(x, y, 2);

The approximation function is then P(1)*x^2 + P(2)*x + P(3)

[Wolfgang McCormack]

@Walter Roberson thank you so much. Three values are calculated for P as array. Now how do I plot it? I want it for both data sets for comparison

I am new and not very much familiar with statistical concepts so I didnot understand what the approximation function is used for

[Walter Roberson]

P = polyfit(x, y, 2);
XI = linspace(min(x), max(x));
YI = polyval(P, XI);
plot(XI, YI, 'k-');

[Wolfgang McCormack]

@Wolfgang McCormack oh THANK YOUUUUU SOOOO MUCHHHHHHHHHHHH! I really don't know how to thank you! I was really frustrated after all my tries. How can I pick your answer as the correct answer?

[Walter Roberson]

You already Accepted my answer, earlier ;-)

[Walter Roberson]

By the way, the way to do it without polyval would have been

P = polyfit(x, y, 2);
XI = linspace(min(x), max(x));
YI = P(1).*XI.^2 + P(2).*XI + P(3);
plot(XI, YI, 'k-');