How to find the intersection of a fitting line with a logarithmic y-axis?
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I have a vector A = [10 40 60 80]
and a vecor B = [5 6 7 8]
I need to create a plot where the x-axis is B and the y-axis is A in the logarithmic scale. Then I need to find the intersection of the fitting line of the scatter with the y-axis.
I used semilogy(B,A) but that only gives me the line and I need to find the intersection.
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Answers (1)
Kevin Holly
on 2 Oct 2021
A= [10 40 60 80];
B = [5 6 7 8];
scatter(B,A,20,'filled')
set(gca,'YScale','log')
% Polyfit
p = polyfit(B,A,2);% 2nd order
f1 = polyval(p,B);
hold on
plot(B,f1,'r--') % poly fit as red dashed line
semilogy(B,A,'g') %log fit as green line
myfit = fittype('a + b*log(x)',...
'dependent',{'y'},'independent',{'x'},...
'coefficients',{'a','b'});
[model stats] = fit(B',A',myfit)
plot(B,model(B),'b') % log fit as blue line
I am not quite sure how to calculate the intersection, but found this:
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