Should fortran-lang.org have a Fortran code snippet on the landing page?

[milancurcic]

What prompted me to open this: https://twitter.com/asmeurer/status/1334423581837561856

When putting together the first version of the website back in April, I wanted and tried to include an example Fortran code snippet. However, at the time, I struggled with my HTML and CSS to make it look pretty so in interest of time I dropped it and moved on. Then I forgot about it.

First question is, should the landing page have an example code syntax, nicely styled, syntax-colored, some minimal but real-world example? The purpose is to show what Fortran looks and feels like, on a first impression to a newcomer to the language.

Second, if the answer is yes (and I think so), can you please think of and propose some example snippets that you think would be good for this? Then we can all discuss them and choose our favorite.

Third, are you interested in making this happen? It should be a relatively low-hanging fruit, with I think a high ROI. It would probably require basic-to-intermediate HTML+CSS skills and a basic sense of good design.

Here are examples for inspiration, some pretty, some not so pretty:

• Python
• Go
• Nim
• Elixir
• Ruby
• Haskell

[milancurcic]

Tagging @asmeurer: What do you think would be a good example and design? Thank you!

[smeskos]

Nice idea, for me, a proper Hello Word example-code for Fortran would be a demonstration of a common and simplified version of a numerical method, eg. Newton-Raphson, or central-difference or something similar that could be written in 5-10 lines.

[certik]

I was going to say what @smeskos suggested: some actual numerical method, that fits into a few lines. About 10 years ago, Travis Oliphant compared a simple vectorized Poisson solver in Python:

http://technicaldiscovery.blogspot.com/2011/06/speeding-up-python-numpy-cython-and.html

and I wrote a version in Fortran:

https://github.com/certik/laplace_test

that was a lot faster: https://github.com/certik/laplace_test/blob/9f0f0c0377642a5d02a386fdda39d51808f75068/laplace_for.f90

So a simplified version could look something like this:

program laplace_example
implicit none
integer, parameter :: dp=kind(0.d0), N = 100
real(dp) :: u(N,N), t1, t2
call cpu_time(t1)
u = laplace(N, 8000, 0.1_dp, 0.1_dp)
call cpu_time(t2)
print *, "Time:", t2 - t1
print *, sum(u), sum(u**2)

contains

    function laplace(N, Niter, dx, dy) result(u)
    integer, intent(in) :: N, Niter
    real(dp), intent(in) :: dx, dy
    real(dp) :: u(N,N)
    integer :: i
    u(1,:) = 1
    u(2:,:) = 0
    do i = 1, Niter
        u(2:N-1,2:N-1) = ((u(3:,2:N-1) + u(:N-2,2:N-1))*dy**2 + &
            (u(2:N-1,3:) + u(2:N-1,:N-2))*dx**2) / (2*(dx**2 + dy**2))
    end do
    end function

end program

Update: I further simplified the code (it still returns the same answer):

program laplace        
implicit none
integer, parameter :: dp=kind(0.d0), N = 100, Niter = 8000
real(dp) :: dx = 0.1_dp, u(N,N), t1, t2
integer :: i
call cpu_time(t1)
u(1,:) = 1
u(2:,:) = 0
do i = 1, Niter
    u(2:N-1,2:N-1) = ((u(3:,2:N-1) + u(:N-2,2:N-1)) + &
        (u(2:N-1,3:) + u(2:N-1,:N-2))) / 4
end do
call cpu_time(t2)
print *, "Time:", t2 - t1
print *, sum(u), sum(u**2)
end program

Or to condense it even further to better fit at the front page:

program laplace
implicit none
integer, parameter :: dp=kind(0.d0), N=100, Niter=8000
real(dp) :: dx=0.1_dp, u(N,N)
integer :: i
u(1,:) = 1; u(2:,:) = 0
do i = 1, Niter
    u(2:N-1,2:N-1) = ((u(3:,2:N-1) + u(:N-2,2:N-1)) + &
        (u(2:N-1,3:) + u(2:N-1,:N-2))) / 4
end do
print *, sum(u), sum(u**2)
end program

Only 12 lines and it is the full program that compiles and runs.

[arjenmarkus]

A Newton-Raphson like example could be written in FORTRAN 77 as well. How about a/my simple qsort example? That would demonstrate array operations as well as non-trivial memory management. Op do 3 dec. 2020 15:50 schreef smeskos <notifications@github.com>:

…

Nice idea, for me, a proper *Hello Word* example-code for Fortran would be a demonstration of a common and simplified version of a numerical method, eg. Newton-Raphson, or central-difference or something similar that could be written in 5-10 lines. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#108>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAN6YR4UDRARF6KHUFDZJVLSS6QUBANCNFSM4UMBJH2Q> .

[certik]

@arjenmarkus, can you post an example that compiles? Let's compare code snippets, then we can effectively select the best one to represent Fortran.

[asmeurer]

Thanks for opening this issue. To me, the most important thing is just to show what the basic syntax looks like. Believe it or not, quite a few people have never actually seen a Fortran program before.

[arjenmarkus]

@Ondřej Čertík <ondrej@certik.us> , well, here is an example: ! qsort_reals.f90 -- ! ! Example belonging to "Modern Fortran in Practice" by Arjen Markus ! ! This work is licensed under the Creative Commons Attribution 3.0 Unported License. ! To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/ ! or send a letter to: ! Creative Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA. ! ! Compact implementation of the QuickSort algorithm ! ! Note: ! Because the function uses Fortran 90 features, its interface should be made ! explicit when using it in an actual program. This is easiest via a module. ! module qsort_functions implicit none contains recursive function qsort_reals( data ) result( sorted ) real, dimension(:), intent(in) :: data real, dimension(1:size(data)) :: sorted if ( size(data) > 1 ) then sorted = & (/ qsort_reals( pack( data(2:), data(2:) > data(1) ) ), & data(1), & qsort_reals( pack( data(2:), data(2:) <= data(1) ) ) /) else sorted = data endif end function qsort_reals end module qsort_functions ! test -- ! Straightforward test ... ! program test_qsort_reals use qsort_functions implicit none real, dimension(200) :: r call random_number( r ) write(*,'(f12.5)') qsort_reals( r ) end program test_qsort_reals Other examples I was thinking about: read a list of numbers, store them in a growing array and then determine basic statistical parameters. Op do 3 dec. 2020 om 18:03 schreef Ondřej Čertík <notifications@github.com>:

…

@arjenmarkus <https://github.com/arjenmarkus>, can you post an example that compiles? Let's compare code snippets, then we can effectively select the best one to represent Fortran. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#108>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAN6YRY6ZWQIMUVCTRQ2P43SS7AEHANCNFSM4UMBJH2Q> .

[certik]

@asmeurer wrote:

Believe it or not, quite a few people have never actually seen a Fortran program before.

Oh, we believe it. That is why where are all here trying to fix it. :) Thank you again for your feedback.

[vmagnin]

Personally, I was very impressed by the Mandelbrot snippet on the Julia page:
https://julialang.org/learning/code-examples/
In 14 lines, they compute and draw a Mandelbrot set in the terminal, like in Mandelbrot days (late 70's)...

But probably concerning Fortran, a short code computing something with array syntax would be better. The @certik Laplace example is interesting, but the loop is difficult to read for someone not familiar with the method. Could be more readable if we put an image of the mathematical writing on the left, and the Fortran algorithm on the right? Fortran is the IBM Mathematical Formula Translating System, isn't it?

[ivan-pi]

Could be more readable if we put an image of the mathematical writing on the left, and the Fortran algorithm on the right? Fortran is the IBM Mathematical Formula Translating System, isn't it?

This is similar to what @rouson and others from the Sourcery Institute have, see here: http://www.sourceryinstitute.org/

I'm not really sure custom unary and binary operators operating on derived types are the most representative element of Fortran though. A more "low level" example using array slicing might be more suitable.

Perhaps an example including co-arrays is another good selling point. Visitors should realize from first sight, that Fortran is a parallel language.

[vmagnin]

Perhaps an example including co-arrays is another good selling point. Visitors should realize from first sight, that Fortran is a parallel language.

Yes, I was also thinking it may be interesting (I am now reading the co-array article). Something with a very modern syntax, with the mathematical formula alongside...