function add(product, left, right) {
  for (var i = 0; i < left.weights.length; i++) {
    product.weights[i] = left.weights[i] + right.weights[i];
    product.deltas[i] = 0;
  }
}
function add(product, left, right) {
  for (var i = 0; i < left.weights.length; i++) {
    product.weights[i] = left.weights[i] + right.weights[i];
    product.deltas[i] = 0;
  }
}
function add ( product , left , right ) { for ( var i = 0 ; i < left . weights . length ; i ++ ) { product . weights [ i ] = left . weights [ i ] + right . weights [ i ] ; product . deltas [ i ] = 0 ; } }
add {left} and {right} matrix weights into {into}
@param {Matrix} product
@param {Matrix} left
@param {Matrix} right
add { left } and { right } matrix weights into { into }
Adds two centric terms