New gtg code compiling option needed

[WenMeng-NOAA]

The gtg code is stored at a NCAR private github repository. Only granted users can check out gtg code as a submodule of UPP at sorc/ post_gtg.fd. UPP needs an option for compiling gtg code from sorc/post_gtg.fd instead of overwriting the stub gtg code at sorc/ncep_post.fd via cmake.

[WenMeng-NOAA]

@junwang-noaa @DusanJovic-NOAA @climbfuji @aerorahul UPP needs help on this new build feature. Would you please let me know your suggestions. Thanks!

[kgerheiser]

Sounds like you want ExternalProject_Add to pass build commands to gtg. How does gtg build (CMake, Makefile, etc)?

[WenMeng-NOAA]

@kgerheiser gtg code along with other UPP code are compiled via CMake. We currently overwrite the stub gtg code (with suffix .F90, e.g. gtg_algo.F90 ) under sorc/ncep_post.fd with real gtg code from sorc/post_gtg.fd.

[aerorahul]

@WenMeng-NOAA
You would build the GTG code in sorc/post_gtg.fd with CMake into a library.
You would build the GTG stub code in sorc/ncep_post.fd with CMake into a library.

When one or the other is available, use the appropriate one to create the UPP library.

[DusanJovic-NOAA]

Another alternative. Since g2g is optional functionality, introduce a build option that enables g2g (optionally ON, OFF by default), then in sorc/ncep_post.fd/CMakeLists.txt use that option to add actual g2g modules to the library, and in the source code where g2g code is used add something like #ifdef G2G_ENABLED to conditionally use g2g module and call 2g2 subroutines. This will eliminate the need for stub code.

[WenMeng-NOAA]

@aerorahul @kgerheiser @DusanJovic-NOAA The gtg code building might have dependency on other general UPP routines. I invite @YaliMao-NOAA in the discussion. She could provide details. We don't have more CMake knowledge. Could we get further guidance? I have an UPP checkout including gtg at /u/Wen.Meng/noscrubd6/ncep_post/develop/UPP/ on Venus. You might use it for testing. Thanks!

[YaliMao-NOAA]

@WenMeng-NOAA You are right, GTG calls some subroutines of the general UPP. It's part of UPP code, not a standalone package.

[aerorahul]

This branch is basically it.
I tried to build the UPP library on wcoss2 with the current develop, but ran into errors in the GTG code.

/lfs/h2/emc/stmp/Rahul.Mahajan/uppWork/upp/sorc/post_gtg.fd/gtg_compute.F90:2351: undefined reference to `defuvp_'
/usr/lib64/gcc/x86_64-suse-linux/7/../../../../x86_64-suse-linux/bin/ld: /lfs/h2/emc/stmp/Rahul.Mahajan/uppWork/upp/sorc/post_gtg.fd/gtg_compute.F90:2

[kgerheiser]

Looks good @aerorahul.

I would also incorporate optionally find/linking to ip based on that option. See #370

[aerorahul]

Looks good @aerorahul.

I would also incorporate optionally find/linking to ip based on that option. See #370

@kgerheiser done in 85138f0

[YaliMao-NOAA]

This branch is basically it. I tried to build the UPP library on wcoss2 with the current develop, but ran into errors in the GTG code.

/lfs/h2/emc/stmp/Rahul.Mahajan/uppWork/upp/sorc/post_gtg.fd/gtg_compute.F90:2351: undefined reference to `defuvp_'
/usr/lib64/gcc/x86_64-suse-linux/7/../../../../x86_64-suse-linux/bin/ld: /lfs/h2/emc/stmp/Rahul.Mahajan/uppWork/upp/sorc/post_gtg.fd/gtg_compute.F90:2

defuvp is defined in map_routines.F90, which is part of GTG code.

[WenMeng-NOAA]

Thanks for all your help! I tested PR #430 on Dell. The executable was successfully built.