Is he? 
$sum += $$x[$i] * $$y[$i] * $$z[$i];

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The above code implies bad things but he is in fact calculating the dot product of 3 vectors that are 2D. To sum it up: not the clearest code ever :-)

In reply to Re^3: Dot product of three matrices by Jaap
in thread Dot product of three matrices by Angharad

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