- dumpMatrix constraint:
  writes scalar LDU matrix coefficients in
  MatrixMarket format

- petscViewMatrix constraint:
  transcribes LDU scalar matrix coefficients into a PETSc AIJ matrix
  format, automatically selecting SeqAIJ or MPIAIJ before opening
  a graphical viewer. Can be used as boilerplate code for other
  PETSc transcription routines.