e.php

        // do the comparison between baseline and current dataset here
        foreach(array('high_rva', 'mid_rva', 'low_rva') as $type) {

            $si = 1;
            
            for($i = 0; $i < count($this->baseline_dataset[$type]); $i++) {

                // calculate Hydrologic Alteration Factor
                $observed_frequency = $this->comparison_dataset[$type][$i];
                $expected_frequency = $this->baseline_dataset[$type][$i] * ($this->years_post / $this->years_pre);
                $divisor = ($expected_frequency > $observed_frequency) ? $expected_frequency : $observed_frequency;
                if ($divisor == 0)
                    $hfa = 0;
                else
                    $hfa = ($observed_frequency - $expected_frequency) / $divisor;

                $this->saveHAF($i, $hfa);

                $hfa_SI = $hfa;

                // SI calc
                
                if ($hfa_SI > 0)
                    $si = $si * $hfa_SI;

                if ($hfa_SI < 0)
                    $si = $si * (-1 * $hfa_SI);

            }
        }