From b90c52e85e9be83d164ba6f801b01fb30097156f Mon Sep 17 00:00:00 2001
From: Josef Hrabal <hrabal.josef@gmail.com>
Date: Sat, 25 Feb 2017 13:32:01 -0500
Subject: [PATCH] Added OpenCoarrays:
docs.it4i/salomon/software/numerical-languages/opencoarrays.md
Added 'Fortran' section under salomon/software/numerical-languages
Added 'OpenCoarrays' page under /salomon/software/numerical-language/fortran
---
.../numerical-languages/opencoarrays.md | 121 ++++++++++++++++++
mkdocs.yml | 2 +
2 files changed, 123 insertions(+)
create mode 100644 docs.it4i/salomon/software/numerical-languages/opencoarrays.md
diff --git a/docs.it4i/salomon/software/numerical-languages/opencoarrays.md b/docs.it4i/salomon/software/numerical-languages/opencoarrays.md
new file mode 100644
index 000000000..d708bf21f
--- /dev/null
+++ b/docs.it4i/salomon/software/numerical-languages/opencoarrays.md
@@ -0,0 +1,121 @@
+# OpenCoarrays
+
+## Introduction
+
+Coarray Fortran (CAF) is an extension of Fortran language and offers a simple interface for parallel processing and memory sharing.
+The advantage is that only small changes are required to convert existing Fortran code to support a robust and potentially efficient parallelism.
+
+A CAF program is interpreted as if it was replicated a number of times and all copies were executed asynchronously.
+The number of copies is decided at execution time. Each copy (called *image*) has its own private variables.
+The variable syntax of Fortran language is extended with indexes in square brackets (called *co-dimension*), which represents a reference to data distributed across images.
+
+By default, the CAF is using Message Passing Interface (MPI) for lower-level communication, so there are some similarities with MPI.
+
+Read more on <http://www.opencoarrays.org/>
+
+### Indexing of coarray images
+
+Indexing of individual images can be shown on the simple *Hello World* program:
+
+```fortran
+ program hello_world
+ implicit none
+ print *, 'Hello world from image ', this_image() , 'of', num_images()
+ end program hello_world
+```
+* num_images() - returns the number of all images
+* this_image() - returns the image index - numbered from 1 to num_images()
+
+### Co-dimension variables declaration
+
+Coarray variables can be declared with the **codimension[*]** attribute or by adding trailing index **[*]** after the variable name.
+Notice, the ***** character always has to be in the square brackets.
+
+```fortran
+ integer, codimension[*] :: scalar
+ integer :: scalar[*]
+ real, dimension(64), codimension[*] :: vector
+ real :: vector(64)[*]
+```
+
+### Images synchronization
+
+Because each image is running on its own, the image synchronization is needed to ensure, that all altered data are distributed to all images.
+Synchronization can be done across all images or only between selected images. Be aware, that selective synchronization can lead to the race condition problems like deadlock.
+
+Example program:
+
+```fortran
+ program synchronization_test
+ implicit none
+ integer :: i ! Local variable
+ integer :: numbers[*] ! Scalar coarray
+
+ ! Genereate random number on image 1
+ if (this_image() == 1) then
+ numbers = floor(rand(1) * 1000)
+ ! Distribute information to other images
+ do i = 2, num_images()
+ numbers[i] = numbers
+ end do
+ end if
+
+ sync all ! Barrier to synchronize all images
+
+ print *, 'The random number is', numbers
+ end program synchronization_test
+```
+
+* sync all - Synchronize all images between each other
+* sync images(*) - Synchronize this image to all other
+* sync images(*index*) - Synchronize this image to image with *index*
+
+!!! note
+ **number** is the local variable while **number[*index*]** accesses the variable in a specific image.
+ **number[this_image()]** is the same as **number**.
+
+### Compiling CAF program
+
+The preferred method for compiling a CAF program is by invoking the *caf* compiler wrapper.
+The above mentioned *Hello World* program can be compiled as follows:
+
+```bash
+ $ caf hello_world.f90 -o hello_world.x
+```
+
+!!! warning
+ The input file extension has to be **.f90** or **.F90** to be interpreted as *Fortran 90*.
+ If the input file extension is **.f** or **.F** the source code will be interpreted as *Fortran 77*.
+
+Another method for compiling is by invoking the *mpif90* compiler wrapper directly:
+
+```bash
+ $ mpif90 hello_world.f90 -o hello_world.x -L $CAF_LIBRARY_PATH -fcoarray=lib -lcaf_mpi
+```
+
+
+### Running CAF program
+
+The preferred method for running a CAF program is by invoking the *cafrun* wrapper:
+
+```bash
+ $ cafrun -np 4 ./hello_world.x
+ Hello world from image 1 of 4
+ Hello world from image 2 of 4
+ Hello world from image 3 of 4
+ Hello world from image 4 of 4
+```
+
+where **-np 4** is number of images to run.
+
+Another method is using the *mpiexec* directly:
+
+```bash
+ $ mpiexec -np 4 ./synchronization_test.x
+ The random number is 242
+ The random number is 242
+ The random number is 242
+ The random number is 242
+```
+
+The parameters of **cafrun** and **mpiexec** are the same.
\ No newline at end of file
diff --git a/mkdocs.yml b/mkdocs.yml
index 0c557765e..216f2b109 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -116,6 +116,8 @@ pages:
- Matlab: salomon/software/numerical-languages/matlab.md
- Octave: salomon/software/numerical-languages/octave.md
- R: salomon/software/numerical-languages/r.md
+ - 'Fortran':
+ - OpenCoarrays: salomon/software/numerical-languages/opencoarrays.md
- Operating System: salomon/software/operating-system.md
- Anselm Software:
- Available Modules: modules-anselm.md
--
GitLab