SQRT17
Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
November 2006
November 2006
Purpose
SQRT17 computes the ratio
|| R'*op(A) ||/(||A||*alpha*max(M,N,NRHS)*eps)
where R = op(A)*X - B, op(A) is A or A', and
alpha = ||B|| if IRESID = 1 (zero-residual problem)
alpha = ||R|| if IRESID = 2 (otherwise).
|| R'*op(A) ||/(||A||*alpha*max(M,N,NRHS)*eps)
where R = op(A)*X - B, op(A) is A or A', and
alpha = ||B|| if IRESID = 1 (zero-residual problem)
alpha = ||R|| if IRESID = 2 (otherwise).
Arguments
| TRANS |
(input) CHARACTER*1
Specifies whether or not the transpose of A is used.
= 'N': No transpose, op(A) = A. = 'T': Transpose, op(A) = A'. |
| IRESID |
(input) INTEGER
IRESID = 1 indicates zero-residual problem.
IRESID = 2 indicates non-zero residual. |
| M |
(input) INTEGER
The number of rows of the matrix A.
If TRANS = 'N', the number of rows of the matrix B. If TRANS = 'T', the number of rows of the matrix X. |
| N |
(input) INTEGER
The number of columns of the matrix A.
If TRANS = 'N', the number of rows of the matrix X. If TRANS = 'T', the number of rows of the matrix B. |
| NRHS |
(input) INTEGER
The number of columns of the matrices X and B.
|
| A |
(input) REAL array, dimension (LDA,N)
The m-by-n matrix A.
|
| LDA |
(input) INTEGER
The leading dimension of the array A. LDA >= M.
|
| X |
(input) REAL array, dimension (LDX,NRHS)
If TRANS = 'N', the n-by-nrhs matrix X.
If TRANS = 'T', the m-by-nrhs matrix X. |
| LDX |
(input) INTEGER
The leading dimension of the array X.
If TRANS = 'N', LDX >= N. If TRANS = 'T', LDX >= M. |
| B |
(input) REAL array, dimension (LDB,NRHS)
If TRANS = 'N', the m-by-nrhs matrix B.
If TRANS = 'T', the n-by-nrhs matrix B. |
| LDB |
(input) INTEGER
The leading dimension of the array B.
If TRANS = 'N', LDB >= M. If TRANS = 'T', LDB >= N. |
| C |
(workspace) REAL array, dimension (LDB,NRHS)
|
| WORK |
(workspace) REAL array, dimension (LWORK)
|
| LWORK |
(input) INTEGER
The length of the array WORK. LWORK >= NRHS*(M+N).
|