Examples of the FORALL Construct

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FORALL ( i=2:n-1, j=2:n-1 )
a(i,j) = a(i,j-1) + a(i,j+1) + a(i-1,j) + a(i+1,j)
b(i,j) = a(i,j)
END FORALL
This `FORALL` is equivalent to the two Fortran 90 statements

a(2:n-1,2:n-1) = a(2:n-1,1:n-2)+a(2:n-1,3:n) &
+a(1:n-2,2:n-1)+a(3:n,2:n-1)
b(2:n-1,2:n-1) = a(2:n-1,2:n-1)
In particular, note that the assignment to array uses the values
of array computed in the first statement, not the values before
the `FORALL` began execution.

FORALL ( i=1:n-1 )
FORALL ( j=i+1:n )
a(i,j) = a(j,i)
END FORALL
END FORALL
This `FORALL` construct
assigns the transpose of the lower triangle of array (i.e., the
section below the main diagonal) to the upper triangle of .
For example, if and originally contained the matrix
then after the `FORALL` it would contain
This cannot be done using array expressions without introducing mask
expressions.

FORALL ( i=1:5 )
WHERE ( a(i,:) .NE. 0.0 )
a(i,:) = a(i-1,:) + a(i+1,:)
ELSEWHERE
b(i,:) = a(6-i,:)
END WHERE
END FORALL
This `FORALL` construct,
when executed with the input arrays
will produce as results
Note that, as with `WHERE` statements in ordinary Fortran 90,
assignments in the `WHERE` branch may affect computations in the
`ELSEWHERE` branch.

*paula@erc.msstate.edu *

Thu Dec 8 16:17:11 CST 1994