Range of possible values for alpha, gamma and eta params of HLDA's Mallet implementation
<p>I'm trying to run the hlda algorytmm and producing a descriptive hierarchy of the input documents. The problem is I'm running diverse parameters configs and trying to understand how it works in an "empirical way", because I can not match the ones that are being used in the original papers (I understand it's a different team). E.g. alpha in Mallet seems to be eta in the paper, but I'm not very sure. Besides, I can not know the boundaries for each of them. I mean, the range of possible values for each parameter.   </p>

<p>In the source code, there is some help:</p>

<pre><code>double alpha; // smoothing on topic distributions
double gamma; // "imaginary" customers at the next
double eta;   // smoothing on word distributions.   
</code></pre>

<p>First, I used the default values: alpha=10.0; gamma=1.0; eta = 0.1;</p>

<p>Then, I tryed running the algorythm by changing the values and interpret the results, but I can't understand the meaning of them. E.g. I think changing gamma (in Mallet) has an effect on the customers decition: to start a new node in the tree or to be placed in an existing one. So, if I set gamma = 0.5, less nodes should be produced, because 0.5 is half the probability of the default one, right? But the results with gamma=1 give me 87 nodes, and with gamma=0.5, it returns 98! And then, I'm asking me something new: is that a probability? I was trying to find the range of possible values in these two papers, but I didn't find them:</p>

<ol>
<li><a href="http://papers.nips.cc/paper/2466-hierarchical-topic-models-and-the-nested-chinese-restaurant-process.pdf" rel="nofollow">Hierarchical Topic Models andthe Nested Chinese Restaurant Process</a></li>
<li><a href="https://cocosci.berkeley.edu/tom/papers/ncrp.pdf" rel="nofollow">The Nested Chinese Restaurant Process and BayesianNonparametric Inference of Topic Hierarchies</a></li>
</ol>

<p>I know I could be missing something, because I don't have the a good background on this, but that's why I'm asking here, maybe someone already had this problem and can help me understanding those limits.</p>

<p>Thanks in advance! </p>