MATLAB: How to code a basic fitting quadratic in this

basic fittingcurve fittingfittingMATLABpolyfitpolyval

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.

Best Answer

P = polyfit(x, y, 2);

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

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MATLAB: Interpolating curve with tangent ends

Hi Michal,

depending on the data, the spline function could give good results. see help spline, where it says that if Y contains two more values than X has entries, then the first and last value in Y are used as the endslopes for the cubic spline.

MATLAB: How to do cubic interpolation from given sets of data

The interp1 function with the 'pchip' method is the easiest way to do this (for me, anyway).

From the documentation:

'pchip' Shape-preserving piecewise cubic interpolation.

The Code —

x=[0 1 8 12 27];
y=[1 2 3 4 5];
xi = linspace(min(x), max(x));
yi = interp1(x, y, xi, 'pchip');
figure(1)
plot(xi, yi)
hold on
plot(x, y, 'pr', 'MarkerFaceColor','g')
hold off
grid

Best Answer

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