Pure Function Example

Consider,

    PURE REAL FUNCTION F(x,y)
     IMPLICIT NONE
     REAL, INTENT(IN) ::  x, y
      F = x*x + y*y + 2*x*y + ASIN(MIN(x/y,y/x))
    END FUNCTION F

Here,

• arguments are unchanged,
• intrinsics are pure so can be used.

Example of use:

    FORALL (i=1:n,j=1:n) &
     A(i,j) = b(i) + F(1.0*i,1.0*j)

Although not mandatory, an explicit interface should be given so that the compiler can witness that the procedure is indeed pure.