TimeWarp.Rand (TimeWarp v0.2.0)

Copy Markdown View Source

Sanctioned, purely-functional seeded PRNG.

Randomness in a model MUST come from a generator carried inside model_state so that (a) two LPs never share a PRNG, coupling their determinism to scheduling, and (b) rollback restores the PRNG position along with the rest of the state snapshot — for free, via structural sharing.

This wraps Erlang's :rand in its explicit-state form (*_s), so there is no hidden per-process seed and nothing to reset on rollback. Never call :rand directly in a model — always thread a %TimeWarp.Rand{} through the state.

Summary

Types

t()

Functions

exponential(r, mean)

Exponentially-distributed value with the given mean, rounded to a positive integer (virtual-time durations). Draws service times, travel durations and inter-arrival gaps.

seed(n)

Seed a fresh generator deterministically from an integer.

uniform(rand)

Uniform float in [0.0, 1.0), plus the advanced generator.

uniform(rand, arg)

Uniform integer in the inclusive range lo..hi, plus the advanced generator.

Types

t()

@type t() :: %TimeWarp.Rand{state: :rand.state()}

Functions

exponential(r, mean)

@spec exponential(t(), number()) :: {pos_integer(), t()}

Exponentially-distributed value with the given mean, rounded to a positive integer (virtual-time durations). Draws service times, travel durations and inter-arrival gaps.

seed(n)

@spec seed(integer()) :: t()

Seed a fresh generator deterministically from an integer.

uniform(rand)

@spec uniform(t()) :: {float(), t()}

Uniform float in [0.0, 1.0), plus the advanced generator.

uniform(rand, arg)

@spec uniform(t(), Range.t()) :: {integer(), t()}

Uniform integer in the inclusive range lo..hi, plus the advanced generator.