ained to be positive.</p>
<p>There are two variants of the exponentiated quadratic covariance
function in Stan. One builds a covariance matrix, <span class="math inline">\(K \in \mathbb{R}^{N \times N}\)</span> for <span class="math inline">\(x_1, \dots, x_N\)</span>, where <span class="math inline">\(K_{i,j} = k(x_i, x_j)\)</span>, which
is necessarily symmetric and positive semidefinite by construction.
There is a second variant of the exponentiated quadratic covariance
function that builds a <span class=