initialize_type_coo Subroutine

    subroutine initialize_type_coo(self, num_nodes, row, col)
        implicit none
        class(type_coo), intent(inout) :: self
        integer(int32), intent(in) :: num_nodes
        integer(int32), intent(in), optional :: row(:)
        integer(int32), intent(in), optional :: col(:)

        integer(int32) :: i

        if (.not. present(row) .or. .not. present(col)) then
            print *, "Error: row and col must be provided for COO initialization."
            stop
        end if

        self%nnz = size(row)

        call allocate_array(self%row, self%nnz)
        do i = 1, self%nnz
            self%row(i) = row(i)
        end do

        call allocate_array(self%col, self%nnz)
        call allocate_array(self%val, self%nnz)
        do i = 1, self%nnz
            self%col(i) = col(i)
            self%val(i) = 0.0d0
        end do

    end subroutine initialize_type_coo