VMAT_lab2_20

program lab2
  implicit none
  integer, parameter :: dim = 8
  integer :: NDIM = dim, N = dim, i,j,k
  real, dimension(dim, dim) :: Q, A, E, RES, C, R, AA
  real :: WORK(dim), COND, V(dim), IPVT(dim), max_sum = 0, sum_el, p = 10.0

  open(1, file="input.txt")

  do i=1,dim
    read(1,*) Q(:,i)
  end do

  close(1)

  do k = 1, 5
    p = p / 10.0
    A = Q
    A(1,1) = A(1,1) + p
    AA = A

    write(*,*) "p = ", p
    call DECOMP(NDIM, N, A, COND, IPVT, WORK)

    E = 0
    forall (j = 1:dim) E(j,j) = 1

    do i=1,dim
      V = 0
      V(i) = 1
      call SOLVE(NDIM, N, A, V, IPVT)
      RES(:,i) = V
    end do

    C = matmul(AA, RES)
    R = E - C

    write(*,*) "Cond = ", COND
    max_sum = 0
    do i=1,dim
      sum_el = 0
        do j=1, dim
          sum_el = sum_el + abs(R(i,j))
        end do
      if (sum_el > max_sum) then
        max_sum = sum_el
      end if
    end do

    write(*,*) "Norm of R matrix = ", max_sum
    write(*,*) "----------------------"
  end do
end program