Then explicit methods could automatically use a solve to apply the mass
matrix inverse for each "right hand side" application and implicit methods
could automatically "drop in" the mass matrix with the shift when a right hand
side Jacobian is given also. Instead of requiring the user to handle this
themselves. Are there any gotcha's that I am missing or is this relatively
straightforward?
Why wouldn't we have this interface?
Note that adjoints are slightly tricky with a mass matrix without this API.
Almost for sure MFEM must have this type of API.
