>pythia81xx</code> directory 
in the file <code>input/mg5_configuration.txt</code>: 
<br/><code>pythia8_path = ./pythia81xx</code>
<br/>The location can be either relative (to the directory
<code>MadGraph5_v_x_x_x/.</code>) or absolute.

<p/>
For any model that is already implemented in the MadGraph 5 package,
you can directly use the model. Start the MadGraph 5 interface
<code>bin/mg5</code>, and do:
<pre>
import model model_name  
generate your_process_in_mg5_syntax 
add process your_next_process_in_mg5_s