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DPTTRF(l)) DPTTRF(l)NAMEDPTTRF - compute the L*D*L' factorization of a real symmetric positive definite tridiago- nal matrix ASYNOPSISSUBROUTINE DPTTRF( N, D, E, INFO ) INTEGER INFO, N DOUBLE PRECISION D( * ), E( * )PURPOSEDPTTRF computes the L*D*L' factorization of a real symmetric positive definite tridiagonal matrix A. The factorization may also be regarded as having the form A = U'*D*U.ARGUMENTSN (input) INTEGER The order of the matrix A. N >= 0. D (input/output) 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' factorization of A. E (input/output) 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' factorization of A. E can also be regarded as the superdiagonal of the unit bidi- agonal factor U from the U'*D*U factorization of A. INFO (output) INTEGER = 0: successful exit < 0: if INFO =, 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.-kLAPACK version 3.015 June 2000 DPTTRF(l)

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