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====== Setting up Parallel VH-1 with NetCDF ======
===== Getting the NetCDF Libraries (v4.2) =====
==== Setting Up NetCDF From Source ====
===== Modifying the Parallel VH-1 Files =====
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June 1-2, 2014: Donald Willcox

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====== Setting up Parallel VH-1 with NetCDF ======
The parallel version of VH-1 uses netcdf, and configuring mpich and netcdf and compiling the parallel version requires installing the following libraries. On Fedora, I installed all of these via ''yum install <library>'' and they are likely available via ''apt-get'' if your Linux distribution uses Synaptic.

  * mpich, mpich-devel
  * netcdf, netcdf-devel
  * netcdf-mpich, netcdf-mpich-devel 
  * netcdf-fortran, netcdf-fortran-devel, netcdf-fortran-mpich, netcdf-fortran-mpich-devel

If for some reason you are unsuccessful in installing netcdf via your package manager, you can install it from source. I had to do this for a remote machine without root access. I'm assuming mpich and the gcc/gfortran build system are already installed.

===== Getting the NetCDF Libraries (v4.2) =====
You can get the source for v.4.2 of the NetCDF Library from Unidata's links as follows:

  * [[http://www.unidata.ucar.edu/downloads/netcdf/ftp/netcdf-4.2.tar.gz]]
  * [[ftp://ftp.unidata.ucar.edu/pub/netcdf/netcdf-fortran-4.2.tar.gz]]
  * [[https://github.com/Unidata/netcdf-cxx4/archive/v4.2.1.tar.gz]]

It depends on hdf5, szip, and zlib libraries, which you can get from:

  * [[http://www.hdfgroup.org/ftp/lib-external/szip/2.1/src/szip-2.1.tar.gz]]
  * [[http://zlib.net/zlib-1.2.8.tar.gz]]
  * [[http://www.hdfgroup.org/ftp/HDF5/releases/hdf5-1.8.12/src/hdf5-1.8.12.tar.gz]]

First, build/install zlib, szip, and hdf5 in that order. Then build/install netcdf-4.2, netcdf-cxx4, and netcdf-fortran-4.2 in that order and you should be good to go. You'll have to set environment variables along the way such as CFLAGS, CPPFLAGS and LDFLAGS to point to the include and lib directories containing the library files you install so that building the library that depends on the previous one can find the appropriate files.

I'll detail that process in the following since getting all this sorted took me a bit of finagling!

==== Setting Up NetCDF From Source ====

I extract the .tar.gz files and then...

For szip and zlib, I used: 

''./configure --prefix=/home/dwillcox/local'' (and then ''make'', ''make check'', ''make install'') 

Then I set the flags as follows:

''export CFLAGS=-I/home/dwillcox/local/include''

''export CPPFLAGS=-I/home/dwillcox/local/include''

''export LDFLAGS=-L/home/dwillcox/local/lib''

That lets hdf5 find those libraries. So in the hdf5 directory I used:

''./configure --enable-fortran --prefix=/home/dwillcox/local/hdf5''

and then ran ''make'', ''make check'', and then ''make install''. I recommend running ''make check'' before ''make install'' because if something is configured improperly, it will fail tests. This happened to me several times before I finally got everything right so it's a nice sanity check.

Then I added the hdf5 location to the flags as follows:

''export CFLAGS=-I/home/dwillcox/local/include -I/home/dwillcox/local/hdf5/include''

''export CPPFLAGS=-I/home/dwillcox/local/include -I/home/dwillcox/local/hdf5/include''

''export LDFLAGS=-L/home/dwillcox/local/lib -L/home/dwillcox/local/hdf5/lib''

Now you can build the netcdf-4.2 library. I used:

''./configure --prefix=/home/dwillcox/local/netcdf --disable-dap''

The ''--disable-dap'' was important because the first time I built and ran ''make check'', it failed a test due to this feature not working properly.

Then I did ''make'', ''make check'', and ''make install'' as usual.

Adding the netcdf locations to the flags is necessary for installing the cxx and fortran versions of netcdf:

''export CFLAGS=-I/home/dwillcox/local/include -I/home/dwillcox/local/hdf5/include -I/home/dwillcox/local/netcdf/include''

''export CPPFLAGS=-I/home/dwillcox/local/include -I/home/dwillcox/local/hdf5/include -I/home/dwillcox/local/netcdf/include''

''export LDFLAGS=-L/home/dwillcox/local/lib -L/home/dwillcox/local/hdf5/lib -L/home/dwillcox/local/netcdf/lib''

With this done, I went to the netcdf-cxx and netcdf-fortran directories and did the following for each of them: 

''./configure --prefix=/home/dwillcox/local/netcdf'', then ''make'', ''make check'', and ''make install''

Finally, I set the following environment variable so building ScientificPython would go smoothly in the "Configuring YT" section!

''export NETCDF_PREFIX=/home/dwillcox/local/netcdf''


===== Modifying the Parallel VH-1 Files =====
The next step is to modify the Makefile in VH1/src/Parallel because it expects to be compiled with Intel's ifort and I'm using gfortran and also because I need to compile mergeslabs.f90, which takes the multiple netcdf files output per timestep and merges them into one. The first modification is to set these flags as follows:

''F90 = mpif90''

''FFLAGS = -c -O3 -Wall -I/usr/include -I/usr/lib64/gfortran/modules''

''LDR= mpif90''

''LDRFLAGS=''

''LIBS= -L/usr/lib64/mpich/lib -lnetcdff -lnetcdf''

Then following the line defining VHOBJS, I added a line as follows:

''MERGEOBJS = mergeslabs.o''

Now, right before the line declaring the clean: target, I declare a target mlabs-mpi which is the binary file I generate by compiling mergeslabs.f90:

''mlabs-mpi:      $(MERGEOBJS)
        
        $(LDR) $(LDRFLAGS) -o mlabs-mpi $(MERGEOBJS) $(LIBS); mv mlabs-mpi ../../output/.''

And finally, declare the dependency for mergeslabs.o by adding the following to the end of the Makefile:

''mergeslabs.o: mergeslabs.f90''

Now, running the Sod shock tube problem requires setting up the geometry and mpi settings. In the Parallel version, the grid geometry specification and initialization is done in init.f90, while specifying how many grid zones to use and how to allocate this to MPI is done in zonemod.f90. So in zonemod.f90 I set ''imax=10, jmax=10, kmax=10'' for a 10x10x10 3D cartesian grid (specified in init.f90). Then I set 2 MPI tasks for the y-dimension (pey=2) and 2 MPI tasks for the z-dimension (pez=2). This means I must run on 2*2=4 processes.

Now ''make'' will put the executable vh1-mpi in the VH1 directory and ''make mlabs-mpi'' will put the executable mlabs-mpi in the VH1/output directory. Run vh1-mpi using ''mpiexec -np 4 ./vh1-mpi'' and then go to VH1/output and run mlabs-mpi. Voila, I've got output for the default 3D Sod shock tube problem and now comes visualizing the data...