A crash course on Fortran

Most of the condensed matter physics codes are written in Fortran and here is a quick summary of Fortran 95 language.

"

! To read a file.

    open(unit=11, file="records.txt", status="old") 
    ! The file is referred to by a 'unit number', an integer that you pick in
    ! the range 9:99. Status can be one of {'old','replace','new'}.
    read(unit=11, fmt="(3F10.2)") a, b, c
    close(11)

    ! To write a file.
    open(unit=12, file="records.txt", status="replace")
    write(12, "(F10.2,F10.2,F10.2)") c, b, a
    close(12)

"

References:
Learn Fortran95 in short duration