Main purpose of FC2K is to embed native code inside Kepler workflow. This way, you are able to connect various, physics based, calculations into chain of execution. There are few rules you have to follow while embedding native code inside Kepler:

• Your routine signature must be exactly the same as one suggested by FC2K
• In order to access IDSes, you have to use IMAS based modules inside your Fortran code
• You can pass data into and outside of the code in the form of:
  • Primitive types
  • IDSes
  • Code parameters
• You should avoid accessing external files unless it's really impossible to run the simulation without external source of data
• All physics related information should be exchanged only via IDSes

In this tutorial, I will show show you how to build simple native code and plug it inside Kepler using FC2K.

Sample, shown below, will access IDS data and print it on console.

1. Preparing the code

First of all, we need simple code that will read data. In this sample, we will use very simple code that reads distribution IDS, shows some info, and output scalar value

Let's say we will retrieve the first time index (as integer) from the array of all times. Remember, this is just an exercise where we want to make all things work together. Don't pay attention to whether it's something meaningful or not. Let's say our actor is supposed to retrieve first time index in the IDS.

IDS -> actor code [we treat the actor as a black box] -> integer

When you talk about actor, most important is the interface. It's API defines how actor interacts with other actors in the workflow.

1.1. What interface should I provide

Let's start with running FC2K. It's little bit counterintuitive, but will help us to properly prepare the code.

First of all, let's add two ports into actor. Input port - IDS, and output port - integer.

Now, let's take a look how the native code should look like in order to provide correct implementation of the actor's API.

Now, once we know how our interface looks like, we can start developing the code

1.2. Source code of the actor

In our case, we can start with providing very basic implementation

subroutine distributiondisp(distributionin, output)
  use ids_schemas
  implicit none
 
  type (ids_distribution_sources) :: distributionin
  integer, intent(out)            :: output
 
  output = int( distributionin%time(1) )  ! we are reading data from the IDS and return it back to Kepler
 
  return
end subroutine

As you can see, we don't even access input data, yet. All we have, so far, is the API of the native code.

1.3. Creating library with native code

As you recall from previous session (dedicated to FC2K) we have to have library that contains native code we are supposed to run.

Let's prepare it. We will do it, by creating Makefile  project - library will be called libdistribution_disp.a 

# In this sample I will use ifort
# However, depending on target system (where IMAS is installed)
# it might be you have other options as well - e.g.: gfortran, pgi, NAG, etc.

F90      = ifort
COPTS    = -g -O0 -assume no2underscore -fPIC -shared-intel

# Note that you should _always_ use pkg-config to obtain
# flags for compiler and linker
# do not pass hardcoded locations unless it's really unavoidable!

LIBS     = `pkg-config --libs imas-ifort imas-lowlevel`
INCLUDES = `pkg-config --cflags imas-ifort imas-lowlevel`

# builds the code that will read IDSed data
all: libdistribution_disp.a

libdistribution_disp.a: distribution_disp.o
	ar -rvs $@ $^

distribution_disp.o: distribution_disp.f90
	$(F90) $(COPTS) -c -o $@ $^ ${INCLUDES} $(LIBS)

# try to provide _clean_ target, so you can easily
# cleanup source tree

clean:
  rm -f *.o *.a

Once we run make we can use library inside the project

> make 
ifort -g -O0 -assume no2underscore -fPIC -shared-intel -c -o distribution_disp.o distribution_disp.f90 `pkg-config --cflags imas-ifort` `pkg-config --libs imas-ifort`
ar -rvs libdistribution_disp.a distribution_disp.o
ar: creating libdistribution_disp.a
a - distribution_disp.o