LR3

      PROGRAM main
      COMMON /size/ N1, ial
      PARAMETER(mem=429496730) !Num of values (1,6GB)
      DIMENSION A(mem) !factual array

c       ia ( 1 : N1+1 )
c       di ( N1+2 : 2*N1+1 )
c       al ( 2*N1+2 : 2*N1+1+ial )
c       vec( 2*N1+2+ial : 3*N1+1+ial )
c       res( 3*N1+2+ial : 4*N1+1+ial )
c       Where ial = ia(N1+1)-1 (number of al() elements)

      BYTE i_read_flag=0      !=1 when the matrix has been read

      CALL menu
    1 READ *, icom
      SELECT CASE (icom)
       CASE (1)
        CALL read_sizes
        CALL dat_to_txt
        CALL input (A(1), A(N1+2), mem)
        i_read_flag=1
        PRINT *, 'Done.'

       CASE (2)
        CALL read_sizes
c       CALL txt_to_dat
        CALL direct_input (A(1), A(N1+2), mem)
        i_read_flag=1
        PRINT *, 'Done.'

       CASE (3)
        IF(i_read_flag .NE. 1) GOTO 3
        CALL multiply (A(1), A(N1+2), A(2*N1+2),
     +  A(2*N1+2+ial), A(3*N1+2+ial))
        CALL output(A(3*N1+ial+2))
        PRINT *, 'Done.'

       CASE (4)
        IF(i_read_flag .NE. 1) GOTO 3
        CALL full_matrix_out(A(1), A(N1+2), A(2*N1+2))
        PRINT *, 'Done.'

       CASE (5)
        CALL generate_matrix
        PRINT *, 'Done.'

       CASE (6)
        GOTO 2

       CASE DEFAULT
        PRINT *, 'Unexpected command.'
        PRINT *, 'Done.'
      END SELECT

      GOTO 1
    3 PRINT *, 'Input the matrix first.'
      GOTO 1
    2 END

      SUBROUTINE menu
      PRINT *, '1. Read matrix from .txt.'
      PRINT *, '2. Read matrix from direct access files.'
      PRINT *, '3. Multyply matrix by vector.'
      PRINT *, '4. Output of the entered matrix in dense format.'
      PRINT *, '5. Generate new matrix (into direct access files).'
      PRINT *, '6. Exit.'
      END

c------------------ Reading matrix and vector dimensions --------------------
      SUBROUTINE read_sizes
      COMMON /size/ N1, ial
      OPEN (1, FILE='N1N2.txt',  ERR=1)

c       N1 - matrix size, N2 - vector size
      READ (1, *) N1, N2
      IF (N1 .ne. N2 .OR. N1 .EQ. 0) STOP 'Matrix N1 != Vector N2.'
      IF (N1 .EQ. 0) STOP 'Matrix size = 0.'

      CLOSE(1)
      GOTO 2
    1 STOP 'Input error: check the input files.'
    2 END

c--------------------- Input data from .txt files ---------------------------
      SUBROUTINE input(ia, A, mem)
      COMMON /size/ N1, ial
c       formal arrays:
      DIMENSION ia(*)
      DIMENSION A(*) ! (di, ia, al, vec)
      OPEN (1, FILE='ia.txt',  ERR=1)
      OPEN (2, FILE='di.txt',  ERR=1)
      OPEN (3, FILE='al.txt',  ERR=1)
      OPEN (4, FILE='vec.txt', ERR=1)

      READ (1, *) (ia(i), i=1, N1+1)                    !ia(N1+1)
      ial=ia(N1+1)-1                           !num of al() elements
      IF(5*N1+ial+1 .GT. mem) STOP 'Not enough memory.'
      READ (2, *) (A(i), i=1, N1)                          !di(N1)
      READ (3, *) (A(i), i=N1+1, N1+ial)         !al(ia(N1+1)-1)
      READ (4, *) (A(i), i=N1+ial+1, 2*N1+ial) !vec(N1)

      CLOSE(1)
      CLOSE(2)
      CLOSE(3)
      CLOSE(4)
      GOTO 2
    1 STOP 'Input error: check the input files.'
    2 END

c------------------ Input data from direct access files ---------------------
      SUBROUTINE direct_input(ia, A, mem)
      COMMON /size/ N1, ial

c       A( di, ia, al, vec )
      DIMENSION ia(*)
      DIMENSION A(*) !formal arrays

      OPEN (1, FILE='ia.dat',  ACCESS='DIRECT', RECL=4, ERR=1)
      OPEN (2, FILE='di.dat',  ACCESS='DIRECT', RECL=4, ERR=1)
      OPEN (3, FILE='al.dat',  ACCESS='DIRECT', RECL=4, ERR=1)
      OPEN (4, FILE='vec.dat', ACCESS='DIRECT', RECL=4, ERR=1)

      DO i=1, N1+1
       READ(1, REC=i) ia(i)
      ENDDO
      ial=ia(N1+1)-1                 !num of al elements
      IF(5*N1+ial+1 .GT. mem) STOP 'Not enough memory.'

      DO i=1, N1
       READ(2, REC=i) A(i)          !di(N1)
      ENDDO

      DO i=1, ial
       READ(3, REC=i) A(N1+i)       !al(ia(N1+1)-1)
      ENDDO

      DO i=1, N1
       READ(4, REC=i) A(N1+ial+i) !vec(N1)
      ENDDO

      CLOSE(1)
      CLOSE(2)
      CLOSE(3)
      CLOSE(4)
      GOTO 2
    1 STOP 'Input error: check the input files.'
    2 END

c--------------- Multiply matrix (profile format) on vector -----------------
      SUBROUTINE multiply (ia, di, al, vec, res)
      COMMON /size/ N1, ial
      DIMENSION ia(*), di(*), al(*), vec(*), res(*)

      DO i=1, N1
       DO j=ia(i), ia(i+1)-1
        ind=i+j-ia(i+1)
        res(i) = res(i) + al(j) * vec(ind)
        res(ind) = res(ind) + al(j) * vec(i)
       ENDDO
       res(i) = res(i) + di(i) * vec(i)
      ENDDO
      END

c-------------------------- Output vector - result --------------------------
      SUBROUTINE output(res)
      COMMON /size/ N1, ial
      DIMENSION res(*)
      OPEN(1, FILE='Result.txt', ERR=1)

      WRITE(1, *)'result = ( '
      DO i=1, N1
       WRITE(1, 10) res(i)
      ENDDO
      WRITE(1, *)')'

      CLOSE(1)
   10 FORMAT(F10.2)
      GOTO 2
    1 STOP 'Output error: check the output file.'
    2 END

c---------------- Full matrix output (99 * 99 max size) -------------------
      SUBROUTINE full_matrix_out(ia, di, al)
      COMMON /size/ N1, ial

      PARAMETER(Nmax=99)
      DIMENSION Fm(Nmax, Nmax)
      DIMENSION ia(*), di(*), al(*)

      DO i=1, N1
       DO j = ia(i), ia(i+1)-1
        ind = i+j-ia(i+1)
        Fm(i, ind) = al(j)
        Fm(ind, i) = al(j)
       ENDDO
       Fm(i, i) = di(i)
      ENDDO

      OPEN (1, FILE='full_matrix.txt', ERR=1)
      DO i=1, N1
       DO j=1, N1
        WRITE(1, 10) Fm(i, j)
       ENDDO
       WRITE (1, 11)
      ENDDO

      CLOSE(1)
      GOTO 2
    1 STOP 'Error: failed to create the output file.'
c   10 FORMAT (F5.2\)
   10 FORMAT(F5.2)
   11 FORMAT (1x)
    2 END

c------------- Generate new matrix (into direct access files) ---------------
      SUBROUTINE generate_matrix

      PRINT *, 'Enter size:'
      PRINT *, '(Or enter 0 to read size of matrix from file.)'
      READ *, m_size
      OPEN(1, FILE = 'N1N2.txt', ERR=1)
      OPEN(2, FILE = 'vec.dat', ACCESS='DIRECT', RECL=4,  ERR=2)
      OPEN(3, FILE = 'di.dat',  ACCESS='DIRECT', RECL=4,  ERR=2)
      OPEN(4, FILE = 'ia.dat',  ACCESS='DIRECT', RECL=4,  ERR=2)
      OPEN(5, FILE = 'al.dat',  ACCESS='DIRECT', RECL=4,  ERR=2)

      IF(m_size .GT. 0) GOTO 5
      READ(1, *) m_size
    5 WRITE(1, 10) m_size, m_size

      DO i = 1, m_size
       WRITE(2, REC=i) i/2.0
       WRITE(3, REC=i) i/10
      ENDDO

      WRITE(4, REC=1) 1
      it = 1
      ik = 1

      DO WHILE (ik .LT. m_size)
       IF (MOD(it, 3) .EQ. 0) GOTO 20
       WRITE(4, REC=ik) it
       ik = ik + 1
20     it = it + 1
      ENDDO
      WRITE(4, REC=ik+1) it

      DO i=1, it
       WRITE(5, REC=i) i/10
      ENDDO

      CLOSE(1)
      CLOSE(2)
      CLOSE(3)
      CLOSE(4)
      CLOSE(5)
      GOTO 3
   10 FORMAT(I2)
    1 STOP 'Error: something went wrong with N1N2.txt'
    2 STOP 'Error: something went wrong with input files.'
    3 END

c-------------- Converting .txt files to direct access files ----------------
      SUBROUTINE txt_to_dat
      COMMON /size/ N1, ial
      PARAMETER(Nmax=999)
      DIMENSION ia(Nmax+1), di(Nmax), al(Nmax*Nmax), vec(Nmax)

      OPEN (1, FILE='ia.txt',  ERR=1)
      OPEN (2, FILE='di.txt',  ERR=1)
      OPEN (3, FILE='al.txt',  ERR=1)
      OPEN (4, FILE='vec.txt', ERR=1)

      OPEN (5, FILE='ia.dat',  ACCESS='DIRECT', RECL=4, ERR=2)
      OPEN (6, FILE='di.dat',  ACCESS='DIRECT', RECL=4, ERR=2)
      OPEN (7, FILE='al.dat',  ACCESS='DIRECT', RECL=4, ERR=2)
      OPEN (8, FILE='vec.dat', ACCESS='DIRECT', RECL=4, ERR=2)

      READ  (1, *) (ia(i), i=1, N1+1)
      DO i=1, N1+1
       WRITE (5, REC=i) ia(i)
      ENDDO
      ial = ia(N1+1)-1

      READ  (2, *) (di(i), i=1, N1)
      DO i=1, N1
       WRITE (6, REC=i) di(i)
      ENDDO

      READ  (3, *) (al(i), i=1, ial)
      DO i=1, ial
       WRITE (7, REC=i) al(i)
      ENDDO

      READ  (4, *) (vec(i), i=1, N1)
      DO i=1, N1
       WRITE (8, REC=i) vec(i)
      ENDDO

      CLOSE(1)
      CLOSE(2)
      CLOSE(3)
      CLOSE(4)
      CLOSE(5)
      CLOSE(6)
      CLOSE(7)
      CLOSE(8)
      GOTO 3
    1 STOP 'Input error: check the input files.'
    2 STOP 'Output error: failed to create direct access file.'
    3 END

c-------------- Converting direct access files to .txt files ----------------
      SUBROUTINE dat_to_txt
      COMMON /size/ N1, ial
      PARAMETER(Nmax=999)
      DIMENSION ia(Nmax+1), di(Nmax), al(Nmax*Nmax), vec(Nmax)

      OPEN (1, FILE='ia.txt',  ERR=1)
      OPEN (2, FILE='di.txt',  ERR=1)
      OPEN (3, FILE='al.txt',  ERR=1)
      OPEN (4, FILE='vec.txt', ERR=1)

      OPEN (5, FILE='ia.dat',  ACCESS='DIRECT', RECL=4, ERR=2)
      OPEN (6, FILE='di.dat',  ACCESS='DIRECT', RECL=4, ERR=2)
      OPEN (7, FILE='al.dat',  ACCESS='DIRECT', RECL=4, ERR=2)
      OPEN (8, FILE='vec.dat', ACCESS='DIRECT', RECL=4, ERR=2)

      DO i=1, N1+1
       READ (5, REC = i) ia(i)
       WRITE (1, *) ia(i)
      ENDDO
      ial = ia(N1+1)-1

      DO i=1, N1
       READ  (6, REC = i) di(i)
       WRITE (2, *) di(i)
      ENDDO

      DO i=1, ial
       READ  (7, REC = i) al(i)
       WRITE (3, *) al(i)
      ENDDO

      DO i=1, N1
       READ  (8, REC = i) vec(i)
       WRITE (4, *) vec(i)
      ENDDO

      CLOSE(1)
      CLOSE(2)
      CLOSE(3)
      CLOSE(4)
      CLOSE(5)
      CLOSE(6)
      CLOSE(7)
      CLOSE(8)
      GOTO 3
    1 STOP 'Input error: check the input files.'
    2 STOP 'Output error: failed to create direct access file.'
    3 END