1SPTTRF(1)                LAPACK routine (version 3.1)                SPTTRF(1)
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NAME

6       SPTTRF - the L*D*L' factorization of a real symmetric positive definite
7       tridiagonal matrix A
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SYNOPSIS

10       SUBROUTINE SPTTRF( N, D, E, INFO )
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12           INTEGER        INFO, N
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14           REAL           D( * ), E( * )
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PURPOSE

17       SPTTRF computes the L*D*L' factorization of a real  symmetric  positive
18       definite  tridiagonal matrix A.  The factorization may also be regarded
19       as having the form A = U'*D*U.
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ARGUMENTS

23       N       (input) INTEGER
24               The order of the matrix A.  N >= 0.
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26       D       (input/output) REAL array, dimension (N)
27               On entry, the n diagonal elements of the tridiagonal matrix  A.
28               On  exit, the n diagonal elements of the diagonal matrix D from
29               the L*D*L' factorization of A.
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31       E       (input/output) REAL array, dimension (N-1)
32               On entry, the (n-1) subdiagonal  elements  of  the  tridiagonal
33               matrix  A.  On exit, the (n-1) subdiagonal elements of the unit
34               bidiagonal factor L from the L*D*L' factorization of A.  E  can
35               also  be  regarded  as the superdiagonal of the unit bidiagonal
36               factor U from the U'*D*U factorization of A.
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38       INFO    (output) INTEGER
39               = 0: successful exit
40               < 0: if INFO = -k, the k-th argument had an illegal value
41               > 0: if INFO = k, the leading minor of order k is not  positive
42               definite;  if  k < N, the factorization could not be completed,
43               while if k = N, the factorization was completed, but D(N) <= 0.
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47 LAPACK routine (version 3.1)    November 2006                       SPTTRF(1)