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The FORALL Statement

Fortran 90 places several restrictions on array assignments. In particular, it requires that operands of the right side expressions be conformable with the left hand side array. These restrictions can be relaxed by introducing the element array assignment statement, usually referred to as the FORALL statement. This statement is used to specify an array assignment in terms of array elements or groups of array sections, possibly masked with a scalar logical expression. In functionality, it is similar to array assignment statements and WHERE statements. The FORALL statement essentially preserves the semantics of Fortran 90 array assignments and allows for convenient assignments like FORALL ( i=1:n, j=1:m ) a(i,j)=i+j as opposed to standard Fortran 90 a = SPREAD((/(i,i=1,n)/), DIM=2, NCOPIES=m) + & SPREAD((/(i,i=1,m)/), DIM=1, NCOPIES=n) It can also express more general array sections than the standard triplet notation for array expressions. For example, FORALL ( i = 1:n ) a(i,i) = b(i) assigns to the elements on the main diagonal of array a.

• []Rationale. It is important to note, however, that FORALL is not intended to be a general parallel construct; for example, it does not express pipelined computations or MIMD computation well. This was an explicit design decision made in order to simplify the construct and promote agreement on the statement's semantics. (End of rationale.)

• General Form of Element Array Assignment
• Interpretation of Element Array Assignments
• Examples of the FORALL Statement
• Scalarization of the FORALL Statement
• Consequences of the Definition of the FORALL Statement