LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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◆ sgttrf()

subroutine sgttrf ( integer n,
real, dimension( * ) dl,
real, dimension( * ) d,
real, dimension( * ) du,
real, dimension( * ) du2,
integer, dimension( * ) ipiv,
integer info )

SGTTRF

Download SGTTRF + dependencies [TGZ] [ZIP] [TXT]

Purpose:
!>
!> SGTTRF computes an LU factorization of a real tridiagonal matrix A
!> using elimination with partial pivoting and row interchanges.
!>
!> The factorization has the form
!>    A = L * U
!> where L is a product of permutation and unit lower bidiagonal
!> matrices and U is upper triangular with nonzeros in only the main
!> diagonal and first two superdiagonals.
!>
Parameters
[in]N
!>          N is INTEGER
!>          The order of the matrix A.
!>
[in,out]DL
!>          DL is REAL array, dimension (N-1)
!>          On entry, DL must contain the (n-1) sub-diagonal elements of
!>          A.
!>
!>          On exit, DL is overwritten by the (n-1) multipliers that
!>          define the matrix L from the LU factorization of A.
!>
[in,out]D
!>          D is REAL array, dimension (N)
!>          On entry, D must contain the diagonal elements of A.
!>
!>          On exit, D is overwritten by the n diagonal elements of the
!>          upper triangular matrix U from the LU factorization of A.
!>
[in,out]DU
!>          DU is REAL array, dimension (N-1)
!>          On entry, DU must contain the (n-1) super-diagonal elements
!>          of A.
!>
!>          On exit, DU is overwritten by the (n-1) elements of the first
!>          super-diagonal of U.
!>
[out]DU2
!>          DU2 is REAL array, dimension (N-2)
!>          On exit, DU2 is overwritten by the (n-2) elements of the
!>          second super-diagonal of U.
!>
[out]IPIV
!>          IPIV is INTEGER array, dimension (N)
!>          The pivot indices; for 1 <= i <= n, row i of the matrix was
!>          interchanged with row IPIV(i).  IPIV(i) will always be either
!>          i or i+1; IPIV(i) = i indicates a row interchange was not
!>          required.
!>
[out]INFO
!>          INFO is INTEGER
!>          = 0:  successful exit
!>          < 0:  if INFO = -k, the k-th argument had an illegal value
!>          > 0:  if INFO = k, U(k,k) is exactly zero. The factorization
!>                has been completed, but the factor U is exactly
!>                singular, and division by zero will occur if it is used
!>                to solve a system of equations.
!>
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.