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How to calculate and plot trendline (fit curve) in matlab?

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Ivan Mich
Ivan Mich on 19 Mar 2021
Answered: Mathieu NOE on 19 Mar 2021
I have one question. I have a X-Y plot. I would like to set the fit curve of this two data (X, Y). But I would like this curve/trendline to be logaritmic. But I did not find it in this link. https://www.mathworks.com/help/curvefit/fit.html
Could you help me please?

Answers (1)

Mathieu NOE
Mathieu NOE on 19 Mar 2021
hello
you can do a curve fit on your data converted to log scale ; here a demo below :
x = [7.94, 16.23, 32.92, 66.8, 135.52, 274.93, 557.78, 1131.59, 2295.72, 4657.46];
y = [134000, 102000, 31000, 11000, 2600, 990, 40, 10.41, 3.48, 1.037];
Bp = polyfit(log10(x), log10(y), 1);
Yp_log = polyval(Bp,log10(x));
figure(1),loglog(x, y, 'pg')
hold on
loglog(x, 10.^Yp_log, '-r')
hold off
grid on
expstr = @(x) [x(:).*10.^ceil(-log10(abs(x(:)))) floor(log10(abs(x(:))))]; % Mantissa & Exponent
Bp2 = expstr(10^Bp(2));
eqn = sprintf('y = %.2f\\times10^{%d}\\cdotx^{%.2f}',Bp2(1), Bp2(2), Bp(1));
legend('Data', eqn)
text(10, 10, strcat('Slope in Log-Log Space =', num2str(Bp(1))), 'Interpreter', 'none');

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