SGBT01
Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
November 2006
November 2006
Purpose
SGBT01 reconstructs a band matrix A from its L*U factorization and
computes the residual:
norm(L*U - A) / ( N * norm(A) * EPS ),
where EPS is the machine epsilon.
The expression L*U - A is computed one column at a time, so A and
AFAC are not modified.
computes the residual:
norm(L*U - A) / ( N * norm(A) * EPS ),
where EPS is the machine epsilon.
The expression L*U - A is computed one column at a time, so A and
AFAC are not modified.
Arguments
| M |
(input) INTEGER
The number of rows of the matrix A. M >= 0.
|
| N |
(input) INTEGER
The number of columns 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.
|
| A |
(input/output) REAL array, dimension (LDA,N)
The original matrix A in band storage, stored in rows 1 to
KL+KU+1. |
| LDA |
(input) INTEGER.
The leading dimension of the array A. LDA >= max(1,KL+KU+1).
|
| AFAC |
(input) REAL array, dimension (LDAFAC,N)
The factored form of the matrix A. AFAC contains the banded
factors L and U from the L*U factorization, as computed by SGBTRF. 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. See SGBTRF for further details. |
| LDAFAC |
(input) INTEGER
The leading dimension of the array AFAC.
LDAFAC >= max(1,2*KL*KU+1). |
| IPIV |
(input) INTEGER array, dimension (min(M,N))
The pivot indices from SGBTRF.
|
| WORK |
(workspace) REAL array, dimension (2*KL+KU+1)
|
| RESID |
(output) REAL
norm(L*U - A) / ( N * norm(A) * EPS )
|