reshape of Fortran
示例
考虑如下代码：
integer,dimension(3,3,2) :: &
mat = reshape( &
(/1,2,3, &
4,5,6 &
7,8,9, &
-1,-2,-3, &
-4,-5,-6, &
-7,-8,-9/),(/3,3,2/))
write(*,*) mat(1,:,1)
write(*,*) mat(2,:,1)
write(*,*) mat(3,:,1)
write(*,*) mat(1,:,2)
write(*,*) mat(2,:,2)
write(*,*) mat(3,:,2)
输出结果为：
1 4 7
2 5 8
3 6 9
-1 -4 -7
-2 -5 -8
-3 -6 -9
若加上参数ORDER：
integer,dimension(3,3,2) :: &
mat = reshape( &
(/1,2,3, &
4,5,6 &
7,8,9, &
-1,-2,-3, &
-4,-5,-6, &
-7,-8,-9/),(/3,3,2/),ORDER=(/3,2,1/))
write(*,*) mat(1,:,1)
write(*,*) mat(2,:,1)
write(*,*) mat(3,:,1)
write(*,*) mat(1,:,2)
write(*,*) mat(2,:,2)
write(*,*) mat(3,:,2)
输出结果为：
1 3 5
7 9 -2
-4 -6 -8
2 4 6
8 -1 -3
-5 -7 -9
建议直观写法为：
integer,dimension(2,3,3) :: &
mat = reshape( &
(/1,2,3, &
4,5,6 &
7,8,9, &
-1,-2,-3, &
-4,-5,-6, &
-7,-8,-9/),(/2,3,3/),ORDER=(/3,2,1/))
write(*,*) mat(1,1,:)
write(*,*) mat(1,2,:)
write(*,*) mat(1,3,:)
write(*,*) mat(2,1,:)
write(*,*) mat(2,2,:)
write(*,*) mat(2,3,:)
此时，输出结果为：
1 2 3
4 5 6
7 8 9
-1 -2 -3
-4 -5 -6
-7 -8 -9
##ORDER 的含义
没有ORDER时，数据按照column-major的方式填充。ORDER=(/1,2,3,…,n/)或者其排列组合(permutation)，n为数组被reshape的维数。
matB = reshape(matA, [n1,n2,n3])
等价于
k = 0
do i3 = 1,n3
do i2 = 1,n2
do i1 = 1,n1
k = k + 1
matB(i1,i2,i3) = matA_seq(k) !matA_seq is a sequential view of matA
end do
end do
end do
加上order这个参数之后：
matB = reshape(matA, [n1,n2,n3], order=[2,3,1])
等价于
k = 0
do i1 = 1,n1
do i3 = 1,n3
do i2 = 1,n2
k = k + 1
matB(i1,i2,i3) = matA_seq(k)
end do
end do
end do