int multivariate_normal_draw(dcovector & X, gsl_rng * r, const dsymatrix & Q){
X.resize(Q.n);
dgematrix L;
int i;
for (i=0;i<X.l;i++)
X(i)=gsl_ran_gaussian(r,1.);
if( cholesky(Q,L)){
X.zero();
return 1;
}
X=L*X;
return 0;
}
int multivariate_normal_draw(dcovector & X, gsl_rng * r, const dgematrix & Q){
X.resize(Q.n);
dgematrix L;
int i;
int j;
int N=Q.m;
dsymatrix S(N);
for (i=0;i<X.l;i++)
X(i)=gsl_ran_gaussian(r,1.);
for (j=0;j<N;j++)
for(i=j;i<N;i++)
S(i,j)=Q(i,j);
if( cholesky(S,L)){
X.zero();
return 1;
}
X=L*X;
return 0;
}