      SUBROUTINE TQLI(D,E,N,NP,Z)
      DOUBLE PRECISION D(NP),E(NP),Z(NP,NP)
      IF (N.GT.1) THEN
        DO 11 I=2,N
          E(I-1)=E(I)
11      CONTINUE
        E(N)=0.
        DO 15 L=1,N
          ITER=0
1         DO 12 M=L,N-1
            DD=ABS(D(M))+ABS(D(M+1))
            IF (ABS(E(M))+DD.EQ.DD) GO TO 2
12        CONTINUE
          M=N
2         IF(M.NE.L)THEN
c            IF(ITER.EQ.30)PAUSE 'too many iterations'
            ITER=ITER+1
            G=(D(L+1)-D(L))/(2.*E(L))
            R=SQRT(G**2+1.)
            G=D(M)-D(L)+E(L)/(G+SIGN(R,G))
            S=1.
            C=1.
            P=0.
            DO 14 I=M-1,L,-1
              F=S*E(I)
              B=C*E(I)
              IF(ABS(F).GE.ABS(G))THEN
                C=G/F
                R=SQRT(C**2+1.)
                E(I+1)=F*R
                S=1./R
                C=C*S
              ELSE
                S=F/G
                R=SQRT(S**2+1.)
                E(I+1)=G*R
                C=1./R  
                S=S*C
              ENDIF
              G=D(I+1)-P
              R=(D(I)-G)*S+2.*C*B
              P=S*R
              D(I+1)=G+P
              G=C*R-B
              DO 13 K=1,N
                F=Z(K,I+1)
                Z(K,I+1)=S*Z(K,I)+C*F
                Z(K,I)=C*Z(K,I)-S*F
13            CONTINUE
14          CONTINUE
            D(L)=D(L)-P
            E(L)=G
            E(M)=0.
            GO TO 1
          ENDIF
15      CONTINUE
      ENDIF
      RETURN
      END
