code: function (v, alpha) {
              this.x += ( v.x - this.x ) * alpha;
              this.y += ( v.y - this.y ) * alpha;
              this.z += ( v.z - this.z ) * alpha;
              return this;
          }
docs: Linearly interpolate between this vector and the given one.
  @name lerp
  @memberOf me.Vector3d
  @function
  @param {me.Vector3d} v
  @param {Number} alpha distance along the line (alpha = 0 will be this vector, and alpha = 1 will be the given one).
  @return {me.Vector3d} Reference to this object for method chaining