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#     Copyright (C) 2012 - 2018  Reza Mohammadi                                                    |
#                                                                                                  |
#     This file is part of BDgraph package.                                                        |
#                                                                                                  |
#     BDgraph is free software: you can redistribute it and/or modify it under                     |
#     the terms of the GNU General Public License as published by the Free                         |
#     Software Foundation; see <https://cran.r-project.org/web/licenses/GPL-3>.                    |
#                                                                                                  |
#     Maintainer: Reza Mohammadi <a.mohammadi@uva.nl>                                              |
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#     Data generator from multivarate normal distribution                                          |
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rmvnorm = function( n = 10, mean = rep( 0, length = ncol( sigma ) ), sigma = diag( length( mean ) ) )
{
    if( !isSymmetric( sigma, tol = sqrt( .Machine$double.eps ), check.attributes = FALSE ) ) 
        stop( "sigma must be a symmetric matrix" )
    
    sigma <- as.matrix( sigma )
    p     <- nrow( sigma )
    if( length( mean ) == 1 ) mean <- rep( mean, p )
    if( length( mean ) != nrow( sigma ) ) stop( "mean and sigma have non-conforming size" )
    
    # - - generate multivariate normal data - - - - - - - - - - - - - - - - - - - - - - - - - - - -|
    chol_sig <- chol( sigma )
    z        <- matrix( stats::rnorm( p * n ), p, n )
    data     <- t( chol_sig ) %*% z + mean
    data     <- t( data )

    return( data )
}