 three decision thresholds:</p>
                            <div class="equation">
                                <code>
                                symbol = {<br>
                                &nbsp;&nbsp;0 if y < threshold1<br>
                                &nbsp;&nbsp;1 if threshold1 ≤ y < threshold2<br>
                                &nbsp;&nbsp;2 if threshold2 ≤ y < threshold3<br>
                                &nbsp;&nbsp;3 if y ≥ threshold3<br>
                                }
     