Forall.md

Forall pattern

A forall is a loop that updates the elements of an array, each iteration updating a different element of the array.

for (int i = 0; i < N; ++i) {
  A[i] = ...
}

A is the array variable and i is the loop index variable, which can be determined at compile-time.

Code examples

C

for (int i = 0; i < n; ++i) {
  D[i] = a * X[i] + Y[i];
} 

Fortran

do i = 1, n
  D(i) = a * X(i) + Y(i)
end do

Parallelizing forall loops with OpenMP and OpenACC

OpenMP and OpenACC provide built-in support for the computation of a forall pattern in parallel. The programmer needs to identify the forall pattern and provide the relevant directives to the compiler (the parallel loop directive in both OpenMP and OpenACC).