Mixed finite element methods for the approximation of time-dependent problems

A given elliptic boundary problem can, in general, be approximated by several different mixed finite element methods, depending on what physical unknowns are most desired. The use of certain mixed methods for time-dependent problems has been proposed by Johnson and Thomee 5]. We analyze here some additional mixed methods for the time-dependent case which can be used to obtain direct approximations to alternate physical quantities of interest.