DGBT02
Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
November 2006
November 2006
Purpose
DGBT02 computes the residual for a solution of a banded system of
equations A*x = b or A'*x = b:
RESID = norm( B - A*X ) / ( norm(A) * norm(X) * EPS).
where EPS is the machine precision.
equations A*x = b or A'*x = b:
RESID = norm( B - A*X ) / ( norm(A) * norm(X) * EPS).
where EPS is the machine precision.
Arguments
| TRANS |
(input) CHARACTER*1
Specifies the form of the system of equations:
= 'N': A *x = b = 'T': A'*x = b, where A' is the transpose of A = 'C': A'*x = b, where A' is the transpose of A |
| 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.
|
| NRHS |
(input) INTEGER
The number of columns of B. NRHS >= 0.
|
| A |
(input) DOUBLE PRECISION 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).
|
| X |
(input) DOUBLE PRECISION array, dimension (LDX,NRHS)
The computed solution vectors for the system of linear
equations. |
| LDX |
(input) INTEGER
The leading dimension of the array X. If TRANS = 'N',
LDX >= max(1,N); if TRANS = 'T' or 'C', LDX >= max(1,M). |
| B |
(input/output) DOUBLE PRECISION array, dimension (LDB,NRHS)
On entry, the right hand side vectors for the system of
linear equations. On exit, B is overwritten with the difference B - A*X. |
| LDB |
(input) INTEGER
The leading dimension of the array B. IF TRANS = 'N',
LDB >= max(1,M); if TRANS = 'T' or 'C', LDB >= max(1,N). |
| RESID |
(output) DOUBLE PRECISION
The maximum over the number of right hand sides of
norm(B - A*X) / ( norm(A) * norm(X) * EPS ). |