code: function (v1, v2) {
                  var dot = v1.dot(v2);
                  // Compute the sum of magnitudes.
                  var length = v1.magnitude() * v2.magnitude();
                  // Normalize the dot product, if necessary.
                  if (!(length === 0) && (length !== 1.0)) {
                      dot /= length;
                  }
  
                  // The normalized dot product should be in the range [-1, 1]. Otherwise the result is an error from
                  // floating point roundoff. So if dot is less than -1 or greater than +1, we treat it as -1 and +1
                  // respectively.
                  if (dot < -1.0) {
                      dot = -1.0;
                  }
                  else if (dot > 1.0) {
                      dot = 1.0;
                  }
  
                  // Angle is arc-cosine of normalized dot product.
                  return Math.acos(dot);
              }
docs: Computes the angle between two Vec3 in radians.
  
  @param {Vec3} v1
  @param {Vec3} v2
  
  @return {Number} The ange in radians