@rnd_exponential(λ:float)
returns a random generator that produces floats \(x\) according to an exponential distribution \(P\) of parameter λ:
P(x | λ) = λ e^(-λ x), x > 0.
See @rnd_bernoulli for a description of random generators.
See also random related functions: @rand, @rand_int, @random, @rnd_bernoulli, @rnd_binomial, @rnd_exponential, @rnd_gamma, @rnd_geometric, @rnd_normal, @rnd_uniform_float, @rnd_uniform_int