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SPTTRF(l)) SPTTRF(l)SPTTRF - compute the L*D*L' factorization of a real symmetric positive definite tridiagonal matrix ANAMESUBROUTINE SPTTRF( N, D, E, INFO ) INTEGER INFO, N REAL D( * ), E( * )SYNOPSISSPTTRF computes the L*D*L' factorization of a real symmetric positive definite tridiagonal matrix A. The fac- torization may also be regarded as having the form A = U'*D*U.PURPOSEN (input) INTEGER The order of the matrix A. N >= 0. D (input/output) REAL 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) REAL 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 bidiagonal factor U from the U'*D*U factorization of A. INFO (output) INTEGER = 0: successful exit < 0: if INFO =ARGUMENTS, 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 SPTTRF(l)

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