 <p>the function <code>Ei</code> does either not exist or is not in your matlab path.</p> <p><strong>Edit:</strong> this function seems to be new in matlab 2011b, so if you are using an older version of matlab, the function won't be there -> error.</p> <p><strong>Edit2:</strong> do you have the <strong>Symbolic Math Toolbox</strong> installed?</p>