Further reading

• Chapter 17 (“Coarrays”) of Modern Fortran Explained: Incorporating Fortran 2018, by Michael Metcalf, John Reid, and Malcolm Cohen, Oxford University Press.
• Parallel Programming with Co-arrays, by Robert W. Numrich, Chapman and Hall/CRC.

Summary

• Fortran refers to any parallel process as an image, whether it’s a physical core or an operating system thread.
• All images execute the same copy of the program in parallel, independent from one another.
• The built-in functions this_image and num_images allow you to identify different images.
• Use these functions in if branches to control the flow of the program for each image.
• Coarrays are the key mechanism for copying data between images.
• Use the sync all statement to synchronize all images.
• The higher the ratio of computation versus communication between images, the more efficient your parallel program will be.