ittle time. What this does is to fit a mixture model
to the data, estimating the mixture proportions. Specifically the model
is that the true effects follow a mixture of multivariate normal
distributions: <span class="math inline">\(B \sim \sum_k \sum_l \pi_{kl}
N(0, \omega_l U_k)\)</span> where the <span class="math inline">\(\omega_l\)</span> are scaling factors set by the
“grid” parameter in <code>mash</code> and the <span class="math inline">\(U_k\)</span> are the covariance matrices (here
specified