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The following hi(generator: random number)generators are available:
center(
table(5)(lllll)(
rowline()
rowfive(Class template)(Integral/Floating point)(Quality)(Speed)(Size of state)
rowline()
rowfive(ti(linear_congruential_engine))(Integral)(Medium)(Medium)(1)
rowfive(ti(subtract_with_carry_engine))(Both)(Medium)(Fast)(25)
rowfive(ti(mersenne_twister_engine))(Integral)(Good)(Fast)(624)
rowline()
))
The ti(linear_congruential_engine) random number generator computes
center(tt(value)+subs(i+1)tt( = OPENPAR+a * value)subs(i)tt( +
c+CLOSEPAR % m))
It expects template arguments for, respectively, the data type to contain
the generated random values; the multiplier tt(a); the additive constant
tt(c); and the modulo value tt(m). Example:
verb( linear_congruential_engine<int, 10, 3, 13> lincon;)
The tt(linear_congruential) generator may be seeded by providing its
constructor with a seeding-argument. E.g., tt(lincon(time(0))).
The ti(subtract_with_carry_engine) random number generator computes
center(tt(value)+subs(i)tt( = OPENPARvalue)+subs(i-s)tt( -
value)+subs(i-r)\
tt( - carry)+subs(i-1)tt(CLOSEPAR % m))
It expects template arguments for, respectively, the data type to contain
the generated random values; the modulo value tt(m); and the subtractive
constants tt(s) and tt(r). Example:
verb( subtract_with_carry_engine<int, 13, 3, 13> subcar;)
The tt(subtract_with_carry_engine) generator may be seeded by providing
its constructor with a seeding-argument. E.g., tt(subcar(time(0))).
The predefined tt(mersenne_twister_engine mt19937) (predefined as type in the
tthi(random) header file) is used in the examples below. It can be constructed
using
hi(mt19937)`tt(mt19937 mt)' or it can be seeded by providing its
constructor with an argument (e.g., tt(mt19937 mt(time(0)))). Its function
call operator returns a random unsigned integral value.
Other ways to initialize the tt(mersenne_twister_engine) are beyond the
scope of the annotations() (but see Lewis+hi(Lewis, P.A.W.) em(et
al.)footnote(
Lewis, P.A.W., Goodman, A.S., and Miller, J.M. (1969), A pseudorandom
number generator for the System/360, IBM Systems Journal, 8, 136-146.) (1969)).
The random number generators may also be seeded by calling their members
tt(seed) accepting tt(unsigned long) values or generator functions (as in
tt(lc.seed(time(0)), lc.seed(mt))).
The random number generators offer members ti(min) and ti(max)
returning, respectively, their minimum and maximum values (inclusive). If a
reduced range is required the generators can be nested in a function or class
adapting the range.
Here's a small example showing how the tt(mersenne_twister_engine
mt19937) can be used to generate random numbers:
verbinsert(-as4 examples/mersenne.cc)
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