DGBCON
Modified to call DLACN2 in place of DLACON, 5 Feb 03, SJH.
Purpose
DGBCON estimates the reciprocal of the condition number of a real
general band matrix A, in either the 1-norm or the infinity-norm,
using the LU factorization computed by DGBTRF.
An estimate is obtained for norm(inv(A)), and the reciprocal of the
condition number is computed as
RCOND = 1 / ( norm(A) * norm(inv(A)) ).
general band matrix A, in either the 1-norm or the infinity-norm,
using the LU factorization computed by DGBTRF.
An estimate is obtained for norm(inv(A)), and the reciprocal of the
condition number is computed as
RCOND = 1 / ( norm(A) * 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.
|
| KL |
(input) INTEGER
The number of subdiagonals within the band of A. KL >= 0.
|
| KU |
(input) INTEGER
The number of superdiagonals within the band of A. KU >= 0.
|
| AB |
(input) DOUBLE PRECISION array, dimension (LDAB,N)
Details of the LU factorization of the band matrix A, as
computed by DGBTRF. U is stored as an upper triangular band matrix with KL+KU superdiagonals in rows 1 to KL+KU+1, and the multipliers used during the factorization are stored in rows KL+KU+2 to 2*KL+KU+1. |
| LDAB |
(input) INTEGER
The leading dimension of the array AB. LDAB >= 2*KL+KU+1.
|
| IPIV |
(input) INTEGER array, dimension (N)
The pivot indices; for 1 <= i <= N, row i of the matrix was
interchanged with row IPIV(i). |
| 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/(norm(A) * norm(inv(A))). |
| WORK |
(workspace) DOUBLE PRECISION array, dimension (3*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 |