text: C $Header$
  C $Name$
  
  CBOP
  C     !ROUTINE: CPP_EEOPTIONS.h
  C     !INTERFACE:
  C     include "CPP_EEOPTIONS.h"
  C
  C     !DESCRIPTION:
  C     *==========================================================*
  C     | CPP\_EEOPTIONS.h                                         |
  C     *==========================================================*
  C     | C preprocessor "execution environment" supporting        |
  C     | flags. Use this file to set flags controlling the        |
  C     | execution environment in which a model runs - as opposed |
  C     | to the dynamical problem the model solves.               |
  C     | Note: Many options are implemented with both compile time|
  C     |       and run-time switches. This allows options to be   |
  C     |       removed altogether, made optional at run-time or   |
  C     |       to be permanently enabled. This convention helps   |
  C     |       with the data-dependence analysis performed by the |
  C     |       adjoint model compiler. This data dependency       |
  C     |       analysis can be upset by runtime switches that it  |
  C     |       is unable to recoginise as being fixed for the     |
  C     |       duration of an integration.                        |
  C     |       A reasonable way to use these flags is to          |
  C     |       set all options as selectable at runtime but then  |
  C     |       once an experimental configuration has been        |
  C     |       identified, rebuild the code with the appropriate  |
  C     |       options set at compile time.                       |
  C     *==========================================================*
  CEOP
  
  #ifndef _CPP_EEOPTIONS_H_
  #define _CPP_EEOPTIONS_H_
  
  C     In general the following convention applies:
  C     ALLOW  - indicates an feature will be included but it may
  C     CAN      have a run-time flag to allow it to be switched
  C              on and off.
  C              If ALLOW or CAN directives are "undef'd" this generally
  C              means that the feature will not be available i.e. it
  C              will not be included in the compiled code and so no
  C              run-time option to use the feature will be available.
  C
  C     ALWAYS - indicates the choice will be fixed at compile time
  C              so no run-time option will be present
  
  C=== Macro related options ===
  C--   Control storage of floating point operands
  C     On many systems it improves performance only to use
  C     8-byte precision for time stepped variables.
  C     Constant in time terms ( geometric factors etc.. )
  C     can use 4-byte precision, reducing memory utilisation and
  C     boosting performance because of a smaller working set size.
  C     However, on vector CRAY systems this degrades performance.
  C     Enable to switch REAL4_IS_SLOW from genmake2 (with LET_RS_BE_REAL4):
  #ifdef LET_RS_BE_REAL4
  #undef REAL4_IS_SLOW
  #else /* LET_RS_BE_REAL4 */
  #define REAL4_IS_SLOW
  #endif /* LET_RS_BE_REAL4 */
  
  C--   Control use of "double" precision constants.
  C     Use D0 where it means REAL*8 but not where it means REAL*16
  #define D0 d0
  
  C=== IO related options ===
  C--   Flag used to indicate whether Fortran formatted write
  C     and read are threadsafe. On SGI the routines can be thread
  C     safe, on Sun it is not possible - if you are unsure then
  C     undef this option.
  #undef FMTFTN_IO_THREAD_SAFE
  
  C--   Flag used to indicate whether Binary write to Local file (i.e.,
  C     a different file for each tile) and read are thread-safe.
  #undef LOCBIN_IO_THREAD_SAFE
  
  C--   Flag to turn off the writing of error message to ioUnit zero
  #undef DISABLE_WRITE_TO_UNIT_ZERO
  
  C--   Alternative formulation of BYTESWAP, faster than
  C     compiler flag -byteswapio on the Altix.
  #undef FAST_BYTESWAP
  
  C--   Flag defined for eeboot_minimal.F, eeset_parms.F and open_copy_data_file.F
  C     to write STDOUT, STDERR and scratch files from process 0 only.
  C WARNING: to use only when absolutely confident that the setup is working
  C     since any message (error/warning/print) from any proc <> 0 will be lost.
  #undef SINGLE_DISK_IO
  
  C=== MPI, EXCH and GLOBAL_SUM related options ===
  C--   Flag turns off MPI_SEND ready_to_receive polling in the
  C     gather_* subroutines to speed up integrations.
  #undef DISABLE_MPI_READY_TO_RECEIVE
  
  C--   Control use of communication that might overlap computation.
  C     Under MPI selects/deselects "non-blocking" sends and receives.
  #define ALLOW_ASYNC_COMMUNICATION
  #undef  ALLOW_ASYNC_COMMUNICATION
  #undef  ALWAYS_USE_ASYNC_COMMUNICATION
  C--   Control use of communication that is atomic to computation.
  C     Under MPI selects/deselects "blocking" sends and receives.
  #define ALLOW_SYNC_COMMUNICATION
  #undef  ALWAYS_USE_SYNC_COMMUNICATION
  
  C--   Control XY periodicity in processor to grid mappings
  C     Note: Model code does not need to know whether a domain is
  C           periodic because it has overlap regions for every box.
  C           Model assume that these values have been
  C           filled in some way.
  #undef  ALWAYS_PREVENT_X_PERIODICITY
  #undef  ALWAYS_PREVENT_Y_PERIODICITY
  #define CAN_PREVENT_X_PERIODICITY
  #define CAN_PREVENT_Y_PERIODICITY
  
  C--   disconnect tiles (no exchange between tiles, just fill-in edges
  C     assuming locally periodic subdomain)
  #undef DISCONNECTED_TILES
  
  C--   Always cumulate tile local-sum in the same order by applying MPI allreduce
  C     to array of tiles ; can get slower with large number of tiles (big set-up)
  #undef GLOBAL_SUM_ORDER_TILES
  
  C--   Alternative way of doing global sum without MPI allreduce call
  C     but instead, explicit MPI send & recv calls. Expected to be slower.
  #undef GLOBAL_SUM_SEND_RECV
  
  C--   Alternative way of doing global sum on a single CPU
  C     to eliminate tiling-dependent roundoff errors. Note: This is slow.
  #undef  CG2D_SINGLECPU_SUM
  
  C=== Other options (to add/remove pieces of code) ===
  C--   Flag to turn on checking for errors from all threads and procs
  C     (calling S/R STOP_IF_ERROR) before stopping.
  #define USE_ERROR_STOP
  
  C--   Control use of communication with other component:
  C     allow to import and export from/to Coupler interface.
  #define COMPONENT_MODULE
  
  #endif /* _CPP_EEOPTIONS_H_ */
  
  #include "CPP_EEMACROS.h"
  
  