Flow manual for the 19.04 release available

A revised reference manual for OPM Flow is now available. Compared to the revision from January, this is a massive update. There is of course the relentless efforts of documenting all the new functionality. What makes this massive is however the inclusion of file format documentation on the output side. You will find EGRID, INIT and RESTART files documented in Appendix D. Another huge thanks to David Baxendale for his relentless efforts keeping the manual in great shape!