Simulate multi-population allele frequencies for independent loci, from a given reference population, following a Dirichlet model. Allele frequencies in the populations are generated as random deviates from a Dirichlet distribution, whose parameters control the deviation of allele frequencies from the values in the reference population.

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`npop` |
the number of populations |

`nloc` |
the number of loci |

`na` |
an integer vector giving the numbers of alleles per locus |

`globalfreq` |
matrix of allele frequencies in the reference population. Data must be given in the format of the Journal of Forensic
Sciences for genetic data. Default corresponds to allele frequencies generated form a Dirichlet distribution
with parameter |

`which.loc` |
which loci to simulate from the |

`alpha1` |
a positive float vector of length |

`alpha2` |
a positive float giving the parameter to be used to in the Dirichlet distribution to generate allele frequencies for the reference population |

In the reference population, allele frequencies for independent loci are simulated using a Dirichlet distribution with
parameter `alpha2`

.

At a given locus L with n alleles, the allele frequencies are modeled as a vector of random
variables p=(p1, ..., pn) following a Dirichlet distribution with a parameter vector of length n,
where each component is equal to alpha2, p1+...+pn=1 and alpha2 > 0.

Note that a more sophisticated generation of global allele frequencies is possible using the `simufreqD`

function.
Similarly, allele frequencies in the independent populations are simulated using a Dirichlet Distribution.
For example, for the first population to simulate, at a given locus L with n alleles,
the allele frequencies are modeled as a vector
of random variables p=(p1, ..., pn) following a Dirichlet distribution with a parameter vector of length n:

(p1(1-a1)/alpha1[1], ..., pn(1-alpha1[1])/alpha1[1]), where p1+...+pn=1 and alpha1[1] > 0.

alpha1[1] is the variance parameter for population 1 and is equivalent to Wright's Fst. The closest this parameter is to one,
the more the population allele frequencies are different from the values of the reference population.

The result is stored in a list with two elements :

`globfreq ` |
a |

`popfreq` |
a |

The code used here for the generation of random Dirichlet deviates was previously implemented in the gtools library.

Hinda Haned contact@hindahaned.info

Nicholson G, Smith AV, Jonsson F, Gustafsson O, Stefansson K, Donnelly P.
Assessing population differentiation and isolation from single-nucleotide polymorphism data.
*J Roy Stat Soc B* 2002;64:695–715

Marchini J, Cardon LR. Discussion on the meeting on "Statistical modelling and analysis of genetic data"
*J Roy Stat Soc B*, 2002;64:740-741

Wright S. The genetical structure of populations. *Ann Eugen* 1951;15:323-354

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