drand - Generate a random double number.
rangen drand -> double
<pre>
SLI ] rngdict /knuthran get 1234567 CreateRNG /rng Set
SLI ] [ 4 ] { pop rng drand } Table ==
[6.922545e-01 1.587092e-01 8.004862e-01 5.062180e-01]
</pre>
drand uses the supplied random number generator to generate
a random number in [0, 1).
/var/www/debian/nest/nest-simulator-2.20.0/lib/sli/librandom.sli