*u*and

_{1}*u*are independent random variables that are uniformly distributed between 0 and 1 and let

_{2}then

*z*and

_{1}*z*are independent random variables with a standard normal distribution. Intuitively, the transformation maps each circle of points around the origin to another circle of points around the origin where larger outer circles are mapped to closely-spaced inner circles and inner circles to outer circles.

_{2}Let's see a Python snippet that implements the transformation:

from numpy import random, sqrt, log, sin, cos, pi from pylab import show,hist,subplot,figure # transformation function def gaussian(u1,u2): z1 = sqrt(-2*log(u1))*cos(2*pi*u2) z2 = sqrt(-2*log(u1))*sin(2*pi*u2) return z1,z2 # uniformly distributed values between 0 and 1 u1 = random.rand(1000) u2 = random.rand(1000) # run the transformation z1,z2 = gaussian(u1,u2) # plotting the values before and after the transformation figure() subplot(221) # the first row of graphs hist(u1) # contains the histograms of u1 and u2 subplot(222) hist(u2) subplot(223) # the second contains hist(z1) # the histograms of z1 and z2 subplot(224) hist(z2) show()The result should be similar to the following:

In the first row of the graph we can see, respectively, the histograms of

*u*and

_{1}*u*before the transformation and in the second row we can see the values after the transformation, respectively

_{2}*z*and

_{1}*z*. We can observe that the values before the transformation are distributed uniformly while the histograms of the values after the transformation have the typical Gaussian shape.

_{2}
how can I use a list of numbers and why are there two random variable?

ReplyDeleteHi Olzhas, in this exapmle u1 and u2 are list of numbers. This will explain you why there are two random variables:

Deletehttps://en.wikipedia.org/wiki/Box%E2%80%93Muller_transform