
#1
May1513, 05:16 AM

P: 2

Hi,
I need to find out how to plot my data with exponential binning. To better see the exponent of f(x) = x ^ \alpha, where x and f(x) are given, I am asked to do exponential binning the data. Would appreciate you help. Yours Atilla 



#2
May1513, 02:31 PM

Sci Advisor
P: 5,935

Use semilog graph paper.




#3
Jun913, 12:54 PM

HW Helper
P: 1,391

It seems the OP hasn't replied, but there are some important issues that need to be addressed here, so I will comment on them for any future posters who stumble across this thread.
If you are generating histograms of something which you expect to follow a power law ##y(x) \sim x^\alpha##, you need to use logarithmic binning, not exponential binning. That is, you want your bins to be equally spaced on a log scale, which means you want the edge of the $k$th bin, B(k), to be given by $$\log_{10}(B(k)) = m \log_{10} (k) + c,$$ where m is the slope and c is the intercept, which are determined by your bin range and your number of bins. For example, if you want 10 bins between 10^{6} and 10^{0}, then ##B(0) = 10^{6}## and ##B(10) = 10^0##, and you can solve for m and c. Now, this next point is extremely important: when using logarithmic binning, you must divide your ydata by the width of the bin. If you do not do this, the power of ##x^\alpha## that you measure will be wrong. Furthermore, when estimating power laws from data, if you need anything more than a rough estimate, a linear regression is a terrible way to find the exponent. It is very prone to systematic errors. Maximum likelihood fits are a much better method. See this preprint for a discussion of properly calculating power laws from data (as well as using hypothesis testing to see if you can rule out other behaviors like lognormal distributions). 



#4
Jun1013, 07:59 AM

P: 2

Exponential binning
Thanks indeed!



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