DGTCON
Modified to call DLACN2 in place of DLACON, 5 Feb 03, SJH.
Purpose
DGTCON estimates the reciprocal of the condition number of a real
tridiagonal matrix A using the LU factorization as computed by
DGTTRF.
An estimate is obtained for norm(inv(A)), and the reciprocal of the
condition number is computed as RCOND = 1 / (ANORM * norm(inv(A))).
tridiagonal matrix A using the LU factorization as computed by
DGTTRF.
An estimate is obtained for norm(inv(A)), and the reciprocal of the
condition number is computed as RCOND = 1 / (ANORM * norm(inv(A))).
Arguments
| NORM |
(input) CHARACTER*1
Specifies whether the 1-norm condition number or the
infinity-norm condition number is required: = '1' or 'O': 1-norm; = 'I': Infinity-norm. |
| N |
(input) INTEGER
The order of the matrix A. N >= 0.
|
| DL |
(input) DOUBLE PRECISION array, dimension (N-1)
The (n-1) multipliers that define the matrix L from the
LU factorization of A as computed by DGTTRF. |
| D |
(input) DOUBLE PRECISION array, dimension (N)
The n diagonal elements of the upper triangular matrix U from
the LU factorization of A. |
| DU |
(input) DOUBLE PRECISION array, dimension (N-1)
The (n-1) elements of the first superdiagonal of U.
|
| DU2 |
(input) DOUBLE PRECISION array, dimension (N-2)
The (n-2) elements of the second superdiagonal of U.
|
| IPIV |
(input) 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. |
| ANORM |
(input) DOUBLE PRECISION
If NORM = '1' or 'O', the 1-norm of the original matrix A.
If NORM = 'I', the infinity-norm of the original matrix A. |
| RCOND |
(output) DOUBLE PRECISION
The reciprocal of the condition number of the matrix A,
computed as RCOND = 1/(ANORM * AINVNM), where AINVNM is an estimate of the 1-norm of inv(A) computed in this routine. |
| WORK |
(workspace) DOUBLE PRECISION array, dimension (2*N)
|
| IWORK |
(workspace) INTEGER array, dimension (N)
|
| INFO |
(output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value |