# std::mersenne_twister_engine::mersenne_twister_engine

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< cpp | numeric | random | mersenne twister engine

mersenne_twister_engine() : mersenne_twister_engine(default_seed) {} |
(1) | (since C++11) |

explicit mersenne_twister_engine( result_type value ); |
(2) | (since C++11) |

template< class Sseq > explicit mersenne_twister_engine( Sseq& s ); |
(3) | (since C++11) |

mersenne_twister_engine( const mersenne_twister_engine& ); |
(4) | (since C++11) (implicitly declared) |

Constructs the pseudo-random number engine.

1) Default constructor. Seeds the engine with

`default_seed`

.2) Constructs the engine and initializes the state (

i of type

is used to initialize X

0 and the rest are initialized iteratively, for i=1-n,...,-1, each X

i is initialized to [f·(X

i-1xor(X

i-1rshift(w-2)))+i mod n] mod 2w

`n`

values Xi of type

`result_type`

) as follows: value mod 2wis used to initialize X

0 and the rest are initialized iteratively, for i=1-n,...,-1, each X

i is initialized to [f·(X

i-1xor(X

i-1rshift(w-2)))+i mod n] mod 2w

3) Constructs the engine and initializes the state by calling s.generate(a, a+n*k) where a is an array of length n*k and k is ceil(w/32) and then, iteratively for i=-n,...,-1, setting each element of the engine state X

i to (Σk-1

j=0a

k(i+n)+j}·232j

) mod 2w

, and finally if the most significant w-r bits of X

0 are zero, and if all other X

i are zero, replacing X

0 with 2w-1

.

i to (Σk-1

j=0a

k(i+n)+j}·232j

) mod 2w

, and finally if the most significant w-r bits of X

0 are zero, and if all other X

i are zero, replacing X

0 with 2w-1

.

Note: initialization requirements are based on the 2002 version of Mersenne Twister, mt19937ar.c

The overload (3) only participates in overload resolution if `Sseq`

qualifies as a SeedSequence. In particular, it is excluded from the set of candidate functions if `Sseq`

is convertible to `result_type`

.

## Contents |

### [edit] Parameters

value | - | seed value to use in the initialization of the internal state |

s | - | seed sequence to use in the initialization of the internal state |

### [edit] Complexity

linear in `n`

(the state size)

### [edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|

P0935R0 | C++11 | default constructor was explicit | made implicit |

### [edit] See also

sets the current state of the engine (public member function) |