nditional and z-i models); <code>psi</code> (extra family parameters, e.g., shape for Tweedie models).</p></dd>


<dt>map</dt>
<dd><p>a list specifying which parameter values should be fixed to a constant value rather than estimated. <code>map</code> should be a named list containing factors corresponding to a subset of the internal parameter names (see <code>start</code> parameter). Distinct factor values are fitted as separate parameter values, <code>NA</code> values are held fixed: e.g., <code>map=list(b