MATLAB: How to perform a polyfit on semilog plot

?slope using polyfit

hi all. i have these two set of data, 'FOE' and 'Nc'. i want to plot FOE vs Nc in semilog plot (Nc placed on x axis increasingly and log scale, FOE on y axis, increasingly). how can i use polyfit command to pass a first order line from this semi-logarithmic graph and obtain slope and interceptof the fitted line. thanks in advance for all the advice you provide.

Best Answer

Try this:
FOE=[0.000743 0.000747 0.000747 0.000746 0.000746 0.000744 0.000744 0.000743 0.00065 0.00065...
    0.000648 0.000648 0.000646 0.000646 0.000644 0.000644 0.000252 0.000252 0.000251 0.000251 0.000251...
    0.000251 0.00025 0.00025 0.000219 0.000219 0.000219 0.000219 0.000218 0.000218 0.000217 0.000217];
Nc=[3.76e-7 8.97e-8 5.09e-8 3.55e-8 2.73e-8 2.22e-8 1.87e-8 1.61e-8 1.42e-8 1.26e-8 1.14e-8 1.04e-8 9.6e-9...
    8.8e-9 8.2e-9 7.7e-9 7.2e-9 6.8e-9 6.4e-9 6.1e-9 5.8e-9 5.5e-9 5.3e-9 5.1e-9 4.8e-9 4.7e-9 4.5e-9 4.3e-9...
    4.2e-9 4e-9 3.9e-9 3.8e-9];
B = polyfit(log(Nc), FOE, 1);
fitFOE = polyval(B,log(Nc));
Slope = B(1);
Intercept = B(2);
figure
semilogx(Nc, FOE, '*',    Nc, fitFOE,'-')
grid
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