The fractional-order diffusion-wave equation is an evolution equation
of order alpha is an element of (0, 2] Which continues to the diffusio
n equation when a --> 1 and to the wave equation when alpha --> 2. We
prove some properties of its solution and give some examples. We defin
e a new fractional calculus (negative-direction fractional calculus) a
nd study some of its properties. We study the existence, uniqueness, a
nd properties of the solution of the negative-direction fractional dif
fusion-wave problem.