Now comput A * ( B * r ) for evaluating expression A * ( B * r ) - ( C * r )
let axbr = new Array ( N ) ; axbr . fill ( 0 ) ; for ( let i = 0 ; i < N ; i ++ ) for ( let j = 0 ; j < N ; j ++ ) axbr [ i ] = axbr [ i ] + a [ i ] [ j ] * br [ j ] ;