SGTTRF
November 2006
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.
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.
Arguments
| N |
(input) INTEGER
The order of the matrix A.
|
| DL |
(input/output) 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. |
| D |
(input/output) 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. |
| DU |
(input/output) 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. |
| DU2 |
(output) REAL array, dimension (N-2)
On exit, DU2 is overwritten by the (n-2) elements of the
second super-diagonal of U. |
| IPIV |
(output) 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. |
| INFO |
(output) 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. |