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 21.2.15 Random Number Generation
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  -- Scheme Procedure: copy-random-state [state]
  -- C Function: scm_copy_random_state (state)
      Return a copy of the random state STATE.
 
  -- Scheme Procedure: random n [state]
  -- C Function: scm_random (n, state)
      Return a number in [0, N).
 
      Accepts a positive integer or real n and returns a number of the
      same type between zero (inclusive) and N (exclusive). The values
      returned have a uniform distribution.
 
      The optional argument STATE must be of the type produced by
      `seed->random-state'. It defaults to the value of the variable
      `*random-state*'. This object is used to maintain the state of the
      pseudo-random-number generator and is altered as a side effect of
      the random operation.
 
  -- Scheme Procedure: random:exp [state]
  -- C Function: scm_random_exp (state)
      Return an inexact real in an exponential distribution with mean 1.
      For an exponential distribution with mean u use (* u
      (random:exp)).
 
  -- Scheme Procedure: random:hollow-sphere! v [state]
  -- C Function: scm_random_hollow_sphere_x (v, state)
      Fills vect with inexact real random numbers the sum of whose
      squares is equal to 1.0.  Thinking of vect as coordinates in space
      of dimension n = (vector-length vect), the coordinates are
      uniformly distributed over the surface of the unit n-sphere.
 
  -- Scheme Procedure: random:normal [state]
  -- C Function: scm_random_normal (state)
      Return an inexact real in a normal distribution.  The distribution
      used has mean 0 and standard deviation 1.  For a normal
      distribution with mean m and standard deviation d use `(+ m (* d
      (random:normal)))'.
 
  -- Scheme Procedure: random:normal-vector! v [state]
  -- C Function: scm_random_normal_vector_x (v, state)
      Fills vect with inexact real random numbers that are independent
      and standard normally distributed (i.e., with mean 0 and variance
      1).
 
  -- Scheme Procedure: random:solid-sphere! v [state]
  -- C Function: scm_random_solid_sphere_x (v, state)
      Fills vect with inexact real random numbers the sum of whose
      squares is less than 1.0.  Thinking of vect as coordinates in
      space of dimension n = (vector-length vect), the coordinates are
      uniformly distributed within the unit n-sphere.  The sum of the
      squares of the numbers is returned.
 
  -- Scheme Procedure: random:uniform [state]
  -- C Function: scm_random_uniform (state)
      Return a uniformly distributed inexact real random number in [0,1).
 
  -- Scheme Procedure: seed->random-state seed
  -- C Function: scm_seed_to_random_state (seed)
      Return a new random state using SEED.
 
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