DPTTRF(3F)DPTTRF(3F)NAME
DPTTRF - compute the factorization of a real symmetric positive definite
tridiagonal matrix A
SYNOPSIS
SUBROUTINE DPTTRF( N, D, E, INFO )
INTEGER INFO, N
DOUBLE PRECISION D( * ), E( * )
PURPOSE
DPTTRF computes the factorization of a real symmetric positive definite
tridiagonal matrix A.
If the subdiagonal elements of A are supplied in the array E, the
factorization has the form A = L*D*L**T, where D is diagonal and L is
unit lower bidiagonal; if the superdiagonal elements of A are supplied,
it has the form A = U**T*D*U, where U is unit upper bidiagonal. (The two
forms are equivalent if A is real.)
ARGUMENTS
N (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**T factorization of A.
E (input/output) DOUBLE PRECISION array, dimension (N-1)
On entry, the (n-1) off-diagonal elements of the tridiagonal
matrix A. On exit, the (n-1) off-diagonal elements of the unit
bidiagonal factor L or U from the factorization of A.
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
> 0: if INFO = i, the leading minor of order i is not positive
definite; if i < N, the factorization could not be completed,
while if i = N, the factorization was completed, but D(N) = 0.
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