s://rdrr.io/r/base/c.html" class="external-link">c</a></span><span class="op">(</span><span class="fl">2</span>,<span class="fl">3</span>,<span class="fl">3</span><span class="op">)</span>, <span class="fl">0</span> <span class="op">)</span></span>
<span><span class="co"># set the following covariances to zero: cov[1,2]=cov[1,3]=cov[2,3]=0</span></span>
<span></span>
<span><span class="co"># estimate model</span></span>
<span><span class="va">mod3</span> <span class="op">&lt;-</span> <span class="fu">sirt</