Matrix-Free Implementation

• support for matrix-free operation essential
• limitations of Fortran 77 required support for matrix-free operation via reverse communication (callback)
  • messy for both host and JTpack77
  • undesirable limitations due to SAVE
• modules and optional arguments allow much cleaner, much more flexible implementation in JTpack90
  • user-defined subroutine for matrix-vector multiplication
  • user-defined subroutine for preconditioning