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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.