Complicated matrix indices

PROGRAM Matrizen2
  IMPLICIT NONE  ! allow no implicit types

  ! constant integers
  INTEGER, PARAMETER :: Ni = 3, Nj = 4, Nk = 100, MAXR = 4
  ! arrays of float64 value, initialized to zero
  DOUBLE PRECISION :: A(Ni, Nk) = 0, B(Ni, Nj) = 0, C(Ni, Nj) = 0
  ! loop counters
  INTEGER :: i, j, k

  ! fill in random numbers in interval [0, 1]
  CALL RANDOM_NUMBER(A)
  CALL RANDOM_NUMBER(B)
  ! make random integers
  A = FLOOR(1 + A * MAXR)  ! rand-int [1, 4]
  B = FLOOR(B * Nk)  ! rand-int [0, Nk]

  ! NOTE: array index starts from 1
  DO i = 1, Ni
     DO j = 1, Nj
        k = INT(B(i, j))
        C(i, j) = A(i, k)
        PRINT '(A2,I0,A1,I0,A4,F6.3)', 'B[', i, ',', j, '] = ', B(i, j)
        PRINT '(A2,I0,A1,I0,A4,F6.3)', 'A[', i, ',', k, '] = ', A(i, k)
        PRINT '(A2,I0,A1,I0,A4,F6.3)', 'C[', i, ',', j, '] = ', C(i, j)
        PRINT *
     END DO
  END DO

END PROGRAM Matrizen2