Introduction to Modern Fortran

This course is aimed at users and developers who know how to program, but have little or no experience in Fortran, and those who may wish to have a refresher in Fortran.

Fortran (a contraction of Formula Translation) was the first programming language to have a standard (in 1954), but has changed significantly over the years. More recent standards (the latest being Fortran 2023) come under the umbrella term "Modern Fortran". Fortran retains very great significance in many areas of scientific and numerical computing, particularly for applications such as quantum chemistry, plasmas, and in numerical weather prediction and climate models.

This course provides an introduction to the basics of writing Fortran. It will cover basic syntax, variables, expressions and assignments, flow of control, and introductions to i/o and user-defined types. Common Fortran idioms are introduced and contrasted with those available in C-like languages; the course will try to focus on real usage rather than formal descriptions.

At the end of the course you should be able to understand many Fortran programs and be confident to start to write well-structured and portable Fortran. Fortran is a rather "large" language, so it is not possible to cover all its features in a two day course. Further elements of Fortran are discussed in the "Intermediate Modern Fortran" course.

Prerequisites: attendees must be familiar with the basic concepts of programming: variables, logic, flow of control, loops, functions and so on. No knowledge of Fortran is assumed. Previous programming experience might typically be in the context C/C++ or python. If you know no programming, we suggest this course on Fortran is not the place to start.

The course requires a Fortran compiler, for which a local machine or laptop may be appropriate [1]. If you do not have access to a Fortran compiler, course training accounts on ARCHER2 will be available which provide access to various compilers. Use of a text editor will be required (some may prefer an IDE, but we do not intend to consider or support IDEs).

[1] This may typically be gfortran, freely available as part of Gnu Compiler Collection (GCC). See e.g., https://gcc.gnu.org/wiki/GFortranBinaries

Installation

For details of how to log into an ARCHER2 account, see https://docs.archer2.ac.uk/quick-start/quickstart-users/

Check out the git repository to your laptop or ARCHER2 account.

$ git clone https://github.com/ARCHER2-HPC/archer2-fortran-intro.git
$ cd archer2-fortran-intro

The default Fortran compiler on ARCHER2 is the Cray Fortran compiler invoked using ftn. For example,

$ cd section1.01
$ ftn example1.f90

should generate an executable with the default name a.out.

Each section of the course is associated with a different directory, each of which contains a number of example programs and exercise templates. Answers to exercises generally re-appear as templates to later exercises. Miscellaneous solutions also appear in the solutions directory.

Not all the examples compile. Some have deliberate errors which will be discussed as part of the course.

Timetable

The timetable may shift slightly in terms of content, but we will stick to the advertised start and finish times, and the break times.

Day one

Time	Content	Section
09:30	Logistics: login, compiler set-up, local details	None
10:00	Background: Fortran standards	FXX
10:20	"Hello World"
	program, print and write, use	section1.01
10:40	Variables: numeric; expressions and assignments, kind
	real, integer, complex, parameter	section1.02
11:00	Break
11:30	Variables: logical, character, conditionals
	if .. end if and select case	section1.03
11:50	Loops and flow of control
	do .. end do, exit and cycle	section2.01
12:30	Exercises
13:00	Lunch
14:00	Array declarations: rank, bounds, size and shape
	dimension, allocatable, allocate(), reshape()	section2.02
14:20	Array expressions: sections, conformance, masks
	minval() etc.; where .. end where; any() all()	section2.03
14:40	Mini-exercise: solve a tri-diagonal system
		section2.04
15:00	Break
15:30	Modules and compilation of modules; scope
	module .. contains .. end module; public, private	section3.01
15:50	Functions and subroutines; dummy argument intent
	function result() subroutine intent ...	section3.02
16:10	More on array dummy arguments; assumed shape, ...
	lbound(), ubound()	section3.03
16:30	Finish

Day two

Time	Content	Section
09:30	More on characters and strings; deferred length
	len() len_trim(), trim()	section4.01
09:50	Format strings and edit descriptors
	read and write	section4.02
10:10	I/O and files; recovering from errors, or not
	open close inquire stop	section4.03
10:30	Exercises
11:00	Break
11:30	Data structures
	type .. end type	section5.01
11:50	Pointer attribute and targets
	null(), associated(), associate .. end associate	section5.02
12:10	Functions: interface blocks, limited polymorphism ...	section6.01
	interface, module procedure
12:30	Miscellaneous intrinsic functions
	get_command_argument(), date_and_time() ...	section6.02
13:00	Lunch
14:00	Mini-exercise on conjugate gradient ...
	.. and larger matrices	section6.03
15:00	Break
15:30	Exercises / solutions
16:00	Other things you may see; testing; resources	section7.01
16:30	Finish

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