Fortran compilers

CAMB internally uses modern (object-oriented) Fortran 2008 for most numerical calculations, and needs a recent fortran compiler to build the numerical library. The recommended compilers are

  • gfortran version 6.3 or higher

  • Intel Fortran (ifort), version 18.0.1 or higher (some things may work with version 14+)

The gfortran compiler is part of the standard “gcc” compiler package, and may be pre-installed on recent unix systems. Check the version using “gfortran –version”.

If you do not have a suitable Fortran compiler, you can get one as follows:

Mac:

Download the binary installation

Windows:

Download gfortran as part of MinGW-w64 (select x86_64 option in the installation program)

Linux:

To install from the standard repository use:

  • “sudo apt-get update; sudo apt-get install gfortran”

On Ubuntu systems where the default gfortran is too old, you can use this to install a later version

  • sudo add-apt-repository ppa:ubuntu-toolchain-r/test

  • sudo apt-get update

  • sudo apt install gfortran-8

To make this the default gfortran then use

  • mkdir -p gfortran-symlinks

  • ln -s /usr/bin/gfortran-8 gfortran-symlinks/gfortran

  • export PATH=$PWD/gfortran-symlinks:$PATH

To re-use next time, add gfortran-symlinks directory to your startup settings (.bashrc).

Alternatively you can compile and run in a container or virtual machine: e.g., see CosmoBox. For example, to run a configured shell in docker where you can install and run camb from the command line (after changing to the camb directory):

docker run -v /local/git/path/CAMB:/camb -i -t cmbant/cosmobox

Updating and modified Fortran code

In the main CAMB source root directory, to re-build the Fortran binary including any pulled or local changes use:

python setup.py make

This will also work on Windows as long as you have MinGW-w64 installed as described above.

Note that you will need to close all python instances using camb before you can re-load with an updated library. This includes in Jupyter notebooks; just re-start the kernel or use:

import IPython
IPython.Application.instance().kernel.do_shutdown(True)

If you want to automamatically rebuild the library from Jupyter you can do something like this:

import subprocess
import sys
import os
src_dir = '/path/to/git/CAMB'
try:
    subprocess.check_output(r'python "%s" make'%os.path.join(src_dir, 'setup.py'),
                            stderr=subprocess.STDOUT)
    sys.path.insert(0,src_dir)
    import camb
    print('Using CAMB %s installed at %s'%(camb.__version__,
                                    os.path.dirname(camb.__file__)))

except subprocess.CalledProcessError as E:
    print(E.output.decode())