说明：  用Mathematica画出了氢原子的电子云。（这里把电子云看做是氢原子的密度分布，而密度分布等于氢原子波函数的模方）
(Mathematica is used to draw the electron cloud of the hydrogen atom. ( the electron cloud is regarded as the density distribution of hydrogen atom, and the density distribution is equal to the modulus of the wave function of the hydrogen atom.))