mirror of
https://github.com/triqs/dft_tools
synced 2024-12-27 23:03:51 +01:00
97 lines
2.9 KiB
ReStructuredText
97 lines
2.9 KiB
ReStructuredText
.. highlight:: c
|
|
|
|
.. _random:
|
|
|
|
Random number generator
|
|
-----------------------
|
|
|
|
Generic use
|
|
***********
|
|
|
|
TRIQS comes with a set of random number generators implemented in the class
|
|
``random_generator``. Here's an example illustrating the
|
|
use of the generator::
|
|
|
|
#include <iostream>
|
|
#include <triqs/mc_tools/random_generator.hpp>
|
|
|
|
int main() {
|
|
|
|
// Construct a random number generator
|
|
triqs::mc_tools::random_generator RNG("mt19937", 23432);
|
|
|
|
// Generate double numbers in [0,1[
|
|
for (size_t i = 0; i < 100; i++) std::cout << RNG() << " ";
|
|
std::cout << std::endl << std::endl;
|
|
|
|
// Generate double numbers in [0,5[
|
|
for (size_t i = 0; i < 100; i++) std::cout << RNG(5.0) << " ";
|
|
std::cout << std::endl << std::endl;
|
|
|
|
// Generate int numbers in [0,5[
|
|
for (size_t i = 0; i < 100; i++) std::cout << RNG(5) << " ";
|
|
std::cout << std::endl << std::endl;
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
After having included the header
|
|
:file:`<triqs/mc_tools/random_generator.hpp>` one constructs a
|
|
random generator with::
|
|
|
|
triqs::mc_tools::random_generator RNG("mt19937", 23432);
|
|
|
|
The first argument is a string which allows you to select the generator. Here
|
|
mt19937 stands for a version of a Mersenne Twister. The second argument is
|
|
the random seed.
|
|
|
|
Now that you have an instance of a generator ``RNG``, you can generate
|
|
either ``double`` numbers or ``int`` numbers. If ``RNG()`` is just called
|
|
with parenthesis, it produces numbers uniformly distributed on the
|
|
interval :math:`[0,1[`. If there is a ``double`` argument ``D``, then
|
|
numbers are produced uniformly on :math:`[0,D]`. Finally, if there is
|
|
a ``int`` argument ``I``, integer numbers are generated on :math:`[0,I[`.
|
|
|
|
|
|
Getting a list of random number generators
|
|
******************************************
|
|
|
|
In order to have a list of all the strings describing the available random
|
|
generators, you can call the static method ``random_generator_names``. For
|
|
example::
|
|
|
|
#include <iostream>
|
|
#include <triqs/mc_tools/random_generator.hpp>
|
|
|
|
int main() {
|
|
|
|
std::cout << "A list of all random generators" << std::endl << std::endl;
|
|
std::cout << triqs::mc_tools::random_generator::random_generator_names() << std::endl;
|
|
|
|
return 0;
|
|
|
|
}
|
|
|
|
|
|
Accessing the random number generator from the Monte Carlo class
|
|
****************************************************************
|
|
|
|
When you construct an instance of a Monte Carlo class ``mc_generic``, this
|
|
instance automatically has an access to a random number generator.
|
|
Imagine you constructed an instance::
|
|
|
|
triqs::mc_tools::mc_generic<double> SpinMC(N_Cycles, Length_Cycle, N_Warmup_Cycles,
|
|
Random_Name, Random_Seed, Verbosity);
|
|
|
|
Now, you can use ``SpinMC`` to have a random number generator::
|
|
|
|
triqs::mc_tools::random_generator RNG = SpinMC.RandomGenerator;
|
|
|
|
Typically, this generator will be passed as a argument to your
|
|
implementation of a move::
|
|
|
|
SpinMC.add_move(mymove(config, SpinMC.RandomGenerator, ...), "my move")
|
|
|
|
|