initialize_type_crs Subroutine

    subroutine initialize_type_crs(self, domain)
        implicit none
        class(type_crs), intent(inout) :: self
        type(type_domain), intent(inout) :: domain

        ! --- ローカル変数 ---
        type(type_coo) :: coo
        integer(int32) :: i, r, pos
        integer(int32), allocatable :: rcm_row(:), rcm_col(:)
        integer(int32), allocatable :: write_pos(:)

        ! =================================================================
        ! Step 1: coo%initializeを呼び出し、COO行列を作成する
        ! =================================================================
        call coo%initialize(domain)

        self%nnz = coo%nnz
        self%num_row = domain%get_num_nodes()
        self%num_ptr = self%num_row + 1

        if (self%nnz == 0) then
            call allocate_array(self%ptr, self%num_ptr)
            self%ptr = 1
            return
        end if

        ! =================================================================
        ! Step 2: COOの行・列インデックスをRCM番号に変換
        ! =================================================================
        call allocate_array(rcm_row, self%nnz)
        call allocate_array(rcm_col, self%nnz)

        call domain%reordering%to_reordered(coo%row, rcm_row)
        call domain%reordering%to_reordered(coo%col, rcm_col)

        ! =================================================================
        ! Step 3: RCM適用後のデータから直接CRS行列を構築
        ! =================================================================
        call allocate_array(self%ptr, self%num_ptr)
        call allocate_array(self%ind, self%nnz)
        call allocate_array(self%val, self%nnz)
        self%ptr = 0

        ! -- Pass 1: 各行の非ゼロ要素数をカウント
        do i = 1, self%nnz
            self%ptr(rcm_row(i) + 1) = self%ptr(rcm_row(i) + 1) + 1
        end do

        ! -- Pass 2: 累積和を計算して、各行の開始ポインタを決定
        self%ptr(1) = 1
        do i = 2, self%num_ptr
            self%ptr(i) = self%ptr(i) + self%ptr(i - 1)
        end do

        ! -- Pass 3: indとvalを正しい位置に配置
        call allocate_array(write_pos, self%num_row)
        write_pos(:) = self%ptr(1:self%num_row)

        do i = 1, self%nnz
            r = rcm_row(i)
            pos = write_pos(r)

            self%ind(pos) = rcm_col(i)
            self%val(pos) = 0.0d0

            write_pos(r) = pos + 1
        end do

        call deallocate_array(write_pos)
        call deallocate_array(rcm_row)
        call deallocate_array(rcm_col)

        call coo%destory()

    end subroutine initialize_type_crs