Hello again.

Regarding this question, if you are using Ubuntu or Debian based distros, you can use apt-get to install it from the main repository.

Enter these commands in the shell:

$ sudo apt-get update

$ sudo apt-get install -y gfortran

You may emit sudo if you are logged in as root.

You might need libgfortran3 ( you will be warned if it is needed ). You can install it with the following command before you install gfortran with commands written above:

$ sudo apt-get install libgfortran3

Again, you may emit sudo if you are logged in as root.

Of course, it is free, because it is GNU.

The parameter -y is just so that apt-get won't ask you a lot of yes/no questions during installation and gfortran is the name of the package.

You could also use the synaptic package manager if you are more comfortable with it rather then using the command line and apt-get (if on Debian family OS).

On Fedora and derived systems, the equivalent command is:

sudo yum install gfortran

or

sudo yum install -y gfortran

this means you have no repository active that provides this package. To help you please give some details on which linux flavour and version you use and which repositories you have installed. A command like "yum repolist" will give you this information, and it can also usually be found the files below /etc/yum.repos.d/

for fedora20 the package name is gcc-gfortran, so this command should work for you:

sudo yum install gcc-gfortran

In addition, I find it convenient to first make a text file that lists all packages that are available: "yum list > package_list.txt".

From this it is easy to use tools like grep to find the exact package name that you need to use for the yum commands.