The FORALL Statement

The FORALL statement allows for more common assignments to sections of an array. A FORALL statement has the general form.

              FORALL ( triplet, ..., triplet,  mask )

                     statement

  where triplet has the general form

                 subscript = lower: upper : step-size

and states a set of indices. step-size is optional. Statement is an pointer or arithmetic assignment and the assignment statement is evaluated for those index values shown by the list of triplets that are not rejected by the optional mask.

Example 7 The following statements set each element of matrix X to the sum of its indices.

 Parallel Programming

 FORALL (i=1:m, j=1:n)     X(i,j) = i+j

and the following statement sets the upper right triangle of  matrix Y to zero .

FORALL (i=1:n, j=1:n, i

Multi-statement FORALL construct:

Multi-statement FORALL is shorthand for the series of single statement FORALLs. The

syntax for FORALL is

FORALL (index-spec-list [,mask]) Body

END FORALL

Nesting of FORALL is allowed.

Example 8

Let a= [2,4,6,8,10], b=[1,3,5,7,9], c=[0,0,0,0,0]

Consider the following program segment

FORALL (i = 2:4) a(i) = a(i-1)+a(i+1) c(i) = b(i) *a(i+1). END FORALL

The computation will be a[2] =a[1]+a[3] =2+6=8 a[3] =a[2]+a[4] =4+8=12 a[4] =a[3]+a[5] = 6+10=16

c[2] = b[2] *a[3] = 3*12=36 c[3] = b[3] *a[4] = 5*16=80

c[4] = b[4] *a[5] =7*10=70

Thus output is

a= [2,8,12,16,10], b=[1,3,5,7,9], c=[0,36,80,70,0]