DPTTRF computes the L*D*L**T factorization of a real symmetric


 positive definite tridiagonal matrix A.  The factorization may also


 be regarded as having the form A = U**T*D*U.

N

          N is INTEGER


          The order of the matrix A.  N >= 0.

D

          D is DOUBLE PRECISION array, dimension (N)


          On entry, the n diagonal elements of the tridiagonal matrix


          A.  On exit, the n diagonal elements of the diagonal matrix


          D from the L*D*L**T factorization of A.

E

          E is DOUBLE PRECISION array, dimension (N-1)


          On entry, the (n-1) subdiagonal elements of the tridiagonal


          matrix A.  On exit, the (n-1) subdiagonal elements of the


          unit bidiagonal factor L from the L*D*L**T factorization of A.


          E can also be regarded as the superdiagonal of the unit


          bidiagonal factor U from the U**T*D*U factorization of A.

INFO

          INFO is INTEGER


          = 0: successful exit


          < 0: if INFO = -k, the k-th argument had an illegal value


          > 0: if INFO = k, the leading minor of order k is not


               positive definite; if k < N, the factorization could not


               be completed, while if k = N, the factorization was


               completed, but D(N) <= 0.

Univ. of Tennessee

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NAG Ltd.

September 2012