title: ichol as cholinc replacement: nonpositive pivot
body: <p>In Matlab 2012 the <code>cholinc</code> command is marked as obsolete. The warning message says it is to be replaced by <code>ichol</code>. Until now I used <code>cholinc(A,droptol)</code>, typically with <code>droptol=1E-15</code>. In the new version I tried to use <code>ichol(A,struct('droptol',droptol,'type','ict'))</code>, which works most of the time, but sometimes I get a warning message</p>
  
  <pre><code>Error using ichol
  Encountered nonpositive pivot.
  </code></pre>
  
  <p>Is this a fundamental problem (i.e. a problem <code>cholinc</code> also had but didn't report) or is there a way to make <code>ichol</code> behave in the way <code>cholinc</code> formerly did?</p>