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<?php function similarity($w1,$w2) { //return cosine similarity of w1 and w2 using formula in the //definition here: http://en.wikipedia.org/wiki/Cosine_similarity //get numerator: $numerator = 0; for($i = 0, $l = count($w1); $i < $l; $i++) $numerator += $w1[$i]*$w2[$i]; //get abs(w1) and abs(w2) $abs_w1 = 0; $abs_w2 = 0; for($i = 0, $l = count($w1); $i < $l; $i++) { $abs_w1 += $w1[i]*$w1[i]; $abs_w2 += $w2[i]*$w2[i]; } $abs_w1 = sqrt($abs_w1); $abs_w2 = sqrt($abs_w2); //make denominator: $denominator = $abs_w1*$abs_w2; return $numerator/$denominator; } similarity([1,2,3,4,5,6,7,8,9],[1,2,3,4,5,6,7,8,88]);