title: glm.nb with sqrt link
body: <p>i'm trying to fit a negbin model with sqrt link. Unfortunately it seems to be that I have to specify starting values. Is anybody familiar with setting starting values when running the <code>glm.nb</code> command (package <code>MASS</code>)?</p>
  
  <p>When I don't use starting values, I get an error message:</p>
  
  <blockquote>
    <p>no valid set of coefficients has been found: please supply starting values</p>
  </blockquote>
  
  <p>Looking at <code>?glm.nb</code> it seems to be possible to set starting values, unfortunately I absolutely don't know how to do this. Some further information: 1.When computing the regression with the standard log link, the regression can be estimated. 2. It is not possible to set the start value for the algorithm to an arbitrary value, so for example</p>
  
  <pre><code>glm.nb(&lt;model&gt;,link=sqrt, start=1)
  </code></pre>
  
  <p>does not work!</p>