Inaccuracy in a loglog(...) plot, compared to a standard plot(...)

Hello,

I have this wierd problem, or I might just be missing something. I have 2 points and I'm trying to interpolate linearly between them. I used a very simple linear interpolation formula, and got the result 2.3672... I confirmed this using an online calculator. However, when plotting the intersection using loglog(...) it seems that the result is around 2.3686... Plotting using the standard plot(...) gives the first, calculated, result. When reading the values of the graphs im zooming very far in, so there is no chance that I misread the values.

I could post the code, but I think the answer has something to do with Matlab's behaviour and not my code. Also I tried using set(gca, 'XScale', 'log', 'YScale', 'log') instead of loglog, still the same results.

Answer 1

[David Goodmanson]

HI Adam,

I am assuming that you are doing something like

x = [1 2]
y = [2,3]
plot(x,y)

and then zooming in on the plot at, say, x = 1.6 to find finding the result y = 2.6. Doing the same thing on a loglog plog gives y = 2.63. But this is not inaccuracy, it's just a different situation. The regular plot draws the straight line y = a + b*x, but the loglog plot draws straight lines in log, so the line is log10(y) = a + b*log10(x) which is a different functional dependence of y on x. So you get a different answer.

[Adam Wisam]

I understand, thank you!