Draw samples from the Laplace or double exponential distribution with
specified location (or mean) and scale (decay).
The Laplace distribution is similar to the Gaussian/normal distribution,
but is sharper at the peak and has fatter tails. It represents the
difference between two independent, identically distributed exponential
random variables.
Parameters : | loc : float
The position,
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, of the distribution peak.
scale : float
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, the exponential decay.
|
Notes
It has the probability density function
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The first law of Laplace, from 1774, states that the frequency of an error
can be expressed as an exponential function of the absolute magnitude of
the error, which leads to the Laplace distribution. For many problems in
Economics and Health sciences, this distribution seems to model the data
better than the standard Gaussian distribution
References
[R199] | Abramowitz, M. and Stegun, I. A. (Eds.). Handbook of Mathematical
Functions with Formulas, Graphs, and Mathematical Tables, 9th
printing. New York: Dover, 1972. |
[R200] | The Laplace distribution and generalizations
By Samuel Kotz, Tomasz J. Kozubowski, Krzysztof Podgorski,
Birkhauser, 2001. |
Examples
Draw samples from the distribution
>>> loc, scale = 0., 1.
>>> s = np.random.laplace(loc, scale, 1000)
Display the histogram of the samples, along with
the probability density function:
>>> import matplotlib.pyplot as plt
>>> count, bins, ignored = plt.hist(s, 30, normed=True)
>>> x = np.arange(-8., 8., .01)
>>> pdf = np.exp(-abs(x-loc/scale))/(2.*scale)
>>> plt.plot(x, pdf)
Plot Gaussian for comparison:
>>> g = (1/(scale * np.sqrt(2 * np.pi)) *
... np.exp( - (x - loc)**2 / (2 * scale**2) ))
>>> plt.plot(x,g)
(Source code, png, pdf)