The necessity of Flux jacobian
 

Hi everyone:

As a cfd beginner I have a question about the flux jacobian.

When I was reading books about cfd, every one of them say something about forming the flux jacobian and solving the eigen values of that. However, I wonder that , if I am using the finite volume explicit solver with central difference scheme, when I should form the flux jacobian and solve the eigen values of that ? I can not figure out why I need this jacobian.