What we are doing is to employ a random number generator to obtain numbers $x_i$ in the interval $[0,1]$ through a call to one of the library functions $ran0$, $ran1$, $ran2$ or $ran3$ which generate random numbers in the interval $x\in [0,1]$. These functions will be discussed in the next section. Here we simply employ these functions in order to generate a random variable. All random number generators produce pseudo-random numbers in the interval $[0,1]$ using the so-called uniform probability distribution $p(x)$ defined as $$\begin{equation*} p(x)=\frac{1}{b-a}\Theta(x-a)\Theta(b-x), \end{equation*}$$ with $a=0$ og $b=1$ and where $\Theta$ is the standard Heaviside function or simply the step function.