翻转矩阵 fortran

Question

我想翻转我的矩阵。使得 T(1,1)=C(2,1)

我已经制作了这个程序，我发现了一个应该在线完成的代码，C=T(2:1:-1, :)但是当尝试获得应该是 3 的值 C(1,1) 时，我得到 1.3533635457363350E-306。你如何翻转矩阵使得向上变成向下？

program main


implicit none
  integer iMax, jMax
  double precision, dimension(:,:), allocatable :: T,C

double precision x, dx,f,L2old,L2norm

integer i, j,n


 allocate(T(0:2, 0:2))
 allocate(C(0:2, 0:2))


T(1,1)=1
T(1,2)=2
T(2,1)=3
T(2,2)=4

write(*,*) T(2,2)

C=T(2:1:-1, :)

Write(*,*) C(1,2)


end program main

Answer 1

如果您分配大小合适的矩阵，那么一切都应该按预期工作。

例如，这个程序

program main
  implicit none

  double precision, dimension(:, :), allocatable :: t, c
  integer :: i

  allocate (t(1:2, 1:2))
  allocate (c(1:2, 1:2))

  t = reshape([1, 3, 2, 4], shape(t))
  do i = 1, 2
    write (*, *) t(i, :)
  end do
  write (*, *) ""

  c = t(2:1:-1, :)
  do i = 1, 2
    write (*, *) c(i, :)
  end do
end program main

产生以下输出

   1.0000000000000000        2.0000000000000000
   3.0000000000000000        4.0000000000000000

   3.0000000000000000        4.0000000000000000
   1.0000000000000000        2.0000000000000000

或者，如果您确实想使用 3x3 矩阵，那么错误就在C=T(2:1:-1, :). 应该是C=T(2:0:-1, :)。

program main
  implicit none

  double precision, dimension(:, :), allocatable :: t, c
  integer :: i

  allocate (t(0:2, 0:2))
  allocate (c(0:2, 0:2))

  t = reshape([1, 4, 7, 2, 5, 8, 3, 6, 9], shape(t))
  do i = 0, 2
    write (*, *) t(i, :)
  end do
  write (*, *) ""

  c = t(2:0:-1, :)
  do i = 0, 2
    write (*, *) c(i, :)
  end do
end program main

输出：

   1.0000000000000000        2.0000000000000000        3.0000000000000000
   4.0000000000000000        5.0000000000000000        6.0000000000000000
   7.0000000000000000        8.0000000000000000        9.0000000000000000

   7.0000000000000000        8.0000000000000000        9.0000000000000000
   4.0000000000000000        5.0000000000000000        6.0000000000000000
   1.0000000000000000        2.0000000000000000        3.0000000000000000

计算数组元素时要小心。关闭接一个错误可能是调试相当困难的，所以最好总是从0从1的帮助下开始计数或始终并成为在安全方面始终遍历数组lbound和ubound内部函数，而不是使用明确的界限，因为它是以上完成：

  do i = lbound(t, dim=1), ubound(t, dim=1)
    write (*, *) t(i, :)
  end do