Example: Calling a Fortran Subroutine for complex arrays in Julia

For this example, say that our Fortran Subroutine in perturbhamiltonian.f90 is responsible for adding an anharmonic term to the Hamiltonian of a 1D-QHO (working in the |n>basis).

We have already written the unperturbed Hamiltonian H with Julia in perturb.jl, but would like to use out existing Fortran-code to add the anharmonic term to the same variable.

Quickstart

After cloning this repository, you can run this example with

make

The end result will be a shared library of the subroutine (.so file) and two text outputs with (almost) identical Hamiltonian data (fortrancall.txt and julia.txt).

Short overview

We need to compile this subroutine as a shared library, (with gfortran we'll have to use the -shared and -fPIC options).

gfortran -shared -fPIC perturbhamiltonian.f90 -o libperturb.so

libperturb.so exposes the PERTURB subroutine to Julia, where it can be called with

# In a Julia session/script
ccall((:perturb_,"./libperturb.so"), Cvoid, (Ref{Int64}, Ref{ComplexF64}, Ref{ComplexF64}), N, lambda, H)

Note that the return type in ccall is set to Cvoid, since we're calling a subroutine (that modifies the input). Care must be taken to specify the correct element types (in the tuple of Refs). For more information on the type correspondences between Julia and C/Fortran, go to the Julia Manual.