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### 21.2.15 Random Number Generation

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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