MATLAB: Polyfit not showing a curve

graphMATLABpolyfitpolynomial

Trying to plot a curve using polyfit. This is my code.
% store coordinates
x = [5.2 5.5 5.6 5.8];
y = [6.408 16.125 19.816 27.912];
% use polyfit to get coefficients of cubic
p = polyfit(x, y, 3);
scatter(x, y, 'black');
hold on
plot(p, 'green');
When plotted, p is jagged and looks nothing like a cubic

Best Answer

polyfit only get you the coefficients, you then have to actually evaluate some values to get the curve. An easy alternative is to use the function polyval (https://de.mathworks.com/help/matlab/ref/polyval.html), which will evaluate the given polynom for the given points. The following code should give you the result you would expect:
% store coordinates
x = [5.2 5.5 5.6 5.8];
y = [6.408 16.125 19.816 27.912];
 
% use polyfit to get coefficients of cubic
p = polyfit(x, y, 3);
yfit = polyval(p,x); % Evaluate polynomial coefficients p in values x
scatter(x, y, 'black');
hold on
plot(x,yfit, 'green');
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