program RestoreCSRdata
    implicit none
    integer, parameter        :: n = 5
    integer                   :: i, j, k, mm, tmp, fileid, first, num
    real(kind=8)              :: matrix(n,n), x(n), a(n,n)
    real(kind=8), allocatable :: aa(:)
    integer, allocatable      :: ia(:), ja(:)
  
    type                      :: node
        real(kind=8)          :: s
        integer               :: k1, k2
        type (node), pointer  :: next
    end type node 
    type (node), pointer      :: head, tail, p, q  
  
    !// input data
    open ( newunit = fileid, file = 'SparseMatrix.txt' )  !// The sparse matrix data needs to be given by itself
    do i = 1, n
            read ( fileid,* ) matrix(i,:)
    end do
    close ( fileid )

    !// =========================store data by CSR format=======================
    first = 1
    if ( .not.associated(p) ) then
        allocate( p )
        q    => p
        nullify( p%next )
        q%k2 = first
        tmp  = q%k2
    end if
  
    num = 0  !// calculate the number of no-zero
    do i =  1, n
        mm = 0  !// calculate the position of no-zero in every row
        do j = i, n
            if ( matrix(i,j) /= 0.0 ) then
                if ( .not.associated(head) ) then
                    allocate( head )
                    tail    => head
                    nullify( tail%next )
                    tail%s  = matrix(i,j)
                    tail%k1 = j
                    num     = num + 1
                    mm      = mm + 1
                else
                    allocate( tail%next )
                    tail    => tail%next
                    tail%s  = matrix(i,j)
                    tail%k1 = j
                    num     = num + 1  
                    mm      = mm + 1  
                    nullify( tail%next )
                end if
            end if
        end do
        if ( associated(p) ) then
            allocate( q%next )
            q    => q%next
            q%k2 = tmp + mm
            tmp  = q%k2
            nullify( q%next )
        end if
    end do
  
    allocate( aa(num), ja(num), ia(n+1) )  !// store the no-zero element
    !// output a and ja
    tail => head
    j = 1
    do 
        if ( .not.associated(tail) ) exit
        aa(j) = tail%s
        ja(j) = tail%k1
        j     = j + 1
        tail  => tail%next
    end do
  
    !// output ia
    q => p
    j = 1
    do 
        if ( .not.associated(q) ) exit
        ia(j) = q%k2
        j     = j + 1
        q     => q%next
    end do
  
    nullify( head, tail, p, q )
    !// =========================store data by CSR format=======================
    write ( *,'(a)' ) '>> Original data'
    write ( *,'(5f7.2)' ) matrix
    write ( *,'(a)' ) '>> CSR data'
    write ( *,'(*(f7.2))' ) aa
    write ( *,'(a)' ) '>> Colnum of CSR data'
    write ( *,'(*(i4))' ) ja
    write ( *,'(a)' ) '>> The position of CSR data'
    write ( *,'(*(i4))' ) ia
  
  
    !// Restore the original array
    a = 0.d0
    j = 0
    do i = 1, n
                    num = ia(i+1) - ia(i)
                    do k = j+1, j+num
                        a(i,ja(k)) = aa(k)
                        a(ja(k),i) = aa(k)
                    end do
                    j = j + num
    end do
    deallocate( aa, ja, ia )
    
    write ( *,'(a)' ) '>> Restore the original array'
    do i = 1, n
            write(*,'(*(f7.2))') a(i,:)
    end do
  
end program RestoreCSRdata

运行结果如下：
>> Original data
   1.00   0.00   0.00   2.00   0.00
   0.00   4.00   0.00   5.00   0.00
   0.00   0.00   7.00   8.00   9.00
   2.00   5.00   8.00  11.00   0.00
   0.00   0.00   9.00   0.00  12.00
>> CSR data
   1.00   2.00   4.00   5.00   7.00   8.00   9.00  11.00  12.00
>> Colnum of CSR data
   1   4   2   4   3   4   5   4   5
>> The position of CSR data
   1   3   5   8   9  10
>> Restore the original array
   1.00   0.00   0.00   2.00   0.00
   0.00   4.00   0.00   5.00   0.00
   0.00   0.00   7.00   8.00   9.00
   2.00   5.00   8.00  11.00   0.00
   0.00   0.00   9.00   0.00  12.00
请按任意键继续. . .