Question

求一个fortran解决线性方程的代码.

补充：用高斯消元法，要求有例子的.

Answer 1

我运行通过了~~
program main
implicit none
integer :: N = 3

real*8 :: A(3,3) = (/ 2, 3, 1, 1, 1, 2, 1, 2, 2 /)
real*8 :: B(3) = (/ 4, 6, 5/), X(3)

call LinearGauss (A, B, X, N)

write(*,*) X

end

!-------------------------------------------------
! 行尺度高斯消元法
!-------------------------------------------------
subroutine LinearGauss (A, B, X, N)
implicit none
integer :: N
real*8 :: A(N, N), B(N), X(N)

real*8 :: z
integer,allocatable :: p(:), s(:)
integer :: i, j, k, sl

allocate (p(N))
allocate (s(N))

do i=1, N
p(i) = i
s(i) = MaxVal ( Abs(A(i, :)) )
end do

do k=1, N-1

j = k
do i=k+1, N
if ( Abs(A(p(j), k)) / s(p(j)) < Abs(A(p(i), k)) / s(p(i)) ) then
j = i
end if
end do
sl = p(k)
p(k) = p(j)
p(j) = sl

do i=k+1, N
z = A(p(i), k) / A(p(k), k)
A(p(i), k) = z
do j=k+1, N
A(p(i), j) = A(p(i), j) - z * A(p(k), j)
end do
end do

end do

do k=1, N-1
do i=k+1, N
B(p(i)) = B(p(i)) - A(p(i), k) * b(p(k))
end do
end do

do i=N, 1, -1
z = 0
do j=i+1, N
z = z + A(p(i), j) * X(j)
end do
X(i) = (B(p(i)) - z) / A(p(i), i)
end do

end subroutine

Answer 2

real*8 :: A(3,3) = (/ 2, 3, 1, 1, 1, 2, 1, 2, 2 /)
real*8 :: B(3) = (/ 4, 6, 5/), X(3)