Wave packets of a harmonic oscillator with various degrees of rigidity
  The time evolution of wave packets in a harmonic oscillator potential is studied. Some new results for the most general case are obtained. A natural number, called ``degree of rigidity'', is introduced to describe qualitatively how much the shape of a wave packet is changed with time. Two classes of wave packets with an arbitrarily given degree of rigidity are presented. 
Qiong-Gui Lin