DECLARE SUB TQLI (D!(), E!(), N!, NP!, Z!())
DECLARE SUB TRED2 (A!(), N!, NP!, D!(), E!())

'PROGRAM D11R4
'Driver for routine TQLI
CLS
NP = 10
TINY = .000001
DIM A(NP, NP), C(NP, NP), D(NP), E(NP), F(NP)
FOR J = 1 TO NP
  FOR I = 1 TO NP
    READ C(I, J)
  NEXT I
NEXT J
DATA 5.0,4.0,3.0,2.0,1.0,0.0,-1.0,-2.0,-3.0,-4.0,4.0,5.0,4.0,3.0,2.0,1.0,0.0
DATA -1.0,-2.0,-3.0,3.0,4.0,5.0,4.0,3.0,2.0,1.0,0.0,-1.0,-2.0,2.0,3.0,4.0,5.0
DATA 4.0,3.0,2.0,1.0,0.0,-1.0,1.0,2.0,3.0,4.0,5.0,4.0,3.0,2.0,1.0,0.0,0.0,1.0
DATA 2.0,3.0,4.0,5.0,4.0,3.0,2.0,1.0,-1.0,0.0,1.0,2.0,3.0,4.0,5.0,4.0,3.0,2.0
DATA -2.0,-1.0,0.0,1.0,2.0,3.0,4.0,5.0,4.0,3.0,-3.0,-2.0,-1.0,0.0,1.0,2.0,3.0
DATA 4.0,5.0,4.0,-4.0,-3.0,-2.0,-1.0,0.0,1.0,2.0,3.0,4.0,5.0
FOR I = 1 TO NP
  FOR J = 1 TO NP
    A(I, J) = C(I, J)
  NEXT J
NEXT I
CALL TRED2(A(), NP, NP, D(), E())
CALL TQLI(D(), E(), NP, NP, A())
PRINT "Eigenvectors for a real symmetric matrix"
FOR I = 1 TO NP
  FOR J = 1 TO NP
    F(J) = 0!
    FOR K = 1 TO NP
      F(J) = F(J) + C(J, K) * A(K, I)
    NEXT K
  NEXT J
  PRINT
  PRINT "Eigenvalue"; I; " =";
  PRINT USING "#####.######"; D(I)
  PRINT
  PRINT "     Vector    Mtrx*Vect.      Ratio"
  FOR J = 1 TO NP
    IF ABS(A(J, I)) < TINY THEN
      PRINT USING "#####.######"; A(J, I); F(J);
      PRINT "       div. by 0"
    ELSE
      PRINT USING "#####.######"; A(J, I); F(J);
      PRINT "     ";
      PRINT USING ".######^^^^"; F(J) / A(J, I)
    END IF
  NEXT J
  PRINT
  PRINT "press ENTER to continue..."
  LINE INPUT DUM$
NEXT I
END