code: func NewBetaGenerator(seed int64) *BetaGenerator {
  	grng1 := NewGammaGenerator(seed)
  	// according to "Numerical Recipes", all distinct
  	//gamma variates must have different random seeds
  	grng2 := NewGammaGenerator(2*seed + 1)
  	return &BetaGenerator{grng1, grng2}
  }
docs: // NewBetaGenerator returns a beta distribution generator
  // it is recommended using time.Now().UnixNano() as the seed, for example:
  // brng := rng.NewBetaGenerator(time.Now().UnixNano())