Error in "birthdeath" function (phylogenetic tree analysis)
<p>I want to determine birth and death rate of a given phylogenetic tree using <code>birthdeath</code> of the <code>ape</code> package, and I get the following error:</p>

<pre class="lang-none prettyprint-override"><code>birthdeath(phy)

Error in solve.default(out$hessian) : 
  Lapack routine dgesv: system is exactly singular: U[1,1] = 0
In addition: Warning messages:
1: In nlm(function(p) dev(p[1], p[2]), c(0.1, 0.2), hessian = TRUE) :
  NA/Inf replaced by maximum positive value
2. etc...
</code></pre>

<p>The tree <code>phy</code> is ultrametric and appears to be fine, <code>checkValidPhylo</code> is true (in particular all edges have positive lengths). It plots just fine and looks normal...</p>

<p>I can upload the tree if need be.</p>