# File vector.rb, line 18
  def *(a)
    if a.class == Vector              # inner product
      product = 0
      self.each_index{|k| product += self[k]*a[k]}
    else
      product = Vector.new           # scalar product
      self.each_index{|k| product[k] = self[k]*a}
    end
    product
  end