Let T be the tridiagonal matrix with diagonal entries A(1) ,...,


    A(N) and offdiagonal entries B(1) ,..., B(N-1)).  SSTECH checks to


    see if EIG(1) ,..., EIG(N) are indeed accurate eigenvalues of T.


    It does this by expanding each EIG(I) into an interval


    [SVD(I) - EPS, SVD(I) + EPS], merging overlapping intervals if


    any, and using Sturm sequences to count and verify whether each


    resulting interval has the correct number of eigenvalues (using


    SSTECT).  Here EPS = TOL*MACHEPS*MAXEIG, where MACHEPS is the


    machine precision and MAXEIG is the absolute value of the largest


    eigenvalue. If each interval contains the correct number of


    eigenvalues, INFO = 0 is returned, otherwise INFO is the index of


    the first eigenvalue in the first bad interval.

N

          N is INTEGER


          The dimension of the tridiagonal matrix T.

A

          A is REAL array, dimension (N)


          The diagonal entries of the tridiagonal matrix T.

B

          B is REAL array, dimension (N-1)


          The offdiagonal entries of the tridiagonal matrix T.

EIG

          EIG is REAL array, dimension (N)


          The purported eigenvalues to be checked.

TOL

          TOL is REAL


          Error tolerance for checking, a multiple of the


          machine precision.

WORK

          WORK is REAL array, dimension (N)

INFO

          INFO is INTEGER


          0  if the eigenvalues are all correct (to within


             1 +- TOL*MACHEPS*MAXEIG)


          >0 if the interval containing the INFO-th eigenvalue


             contains the incorrect number of eigenvalues.

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