LagrangeInterpolation.php

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<?php

require_once "../Matrix.php";

class LagrangeInterpolation {

        public function findPolynomialFactors($x, $y) {
                $n = count($x);

                $data = array();  // double[n][n];
                $rhs  = array();  // double[n];

                for ($i = 0; $i < $n; ++$i) {
                        $v = 1;
                        for ($j = 0; $j < $n; ++$j) {
                                $data[$i][$n-$j-1] = $v;
                                $v *= $x[$i];
                        }
                        $rhs[$i] = $y[$i];
                }

                // Solve m * s = b
                $m = new Matrix($data);
                $b = new Matrix($rhs, $n);

                $s = $m->solve($b);

                return $s->getRowPackedCopy();
        }       //      function findPolynomialFactors()

}       //      class LagrangeInterpolation


$x = array(2.0, 1.0, 3.0);
$y = array(3.0, 4.0, 7.0);

$li = new LagrangeInterpolation;
$f = $li->findPolynomialFactors($x, $y);


for ($i = 0; $i < 3; ++$i) {
        echo $f[$i]."<br />";
}