LAPACK  3.5.0
LAPACK: Linear Algebra PACKage
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dqrt17.f File Reference

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Functions/Subroutines

DOUBLE PRECISION function dqrt17 (TRANS, IRESID, M, N, NRHS, A, LDA, X, LDX, B, LDB, C, WORK, LWORK)
 DQRT17

Function/Subroutine Documentation

DOUBLE PRECISION function dqrt17 ( character  TRANS,
integer  IRESID,
integer  M,
integer  N,
integer  NRHS,
double precision, dimension( lda, * )  A,
integer  LDA,
double precision, dimension( ldx, * )  X,
integer  LDX,
double precision, dimension( ldb, * )  B,
integer  LDB,
double precision, dimension( ldb, * )  C,
double precision, dimension( lwork )  WORK,
integer  LWORK 
)

DQRT17

Purpose:
 DQRT17 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).
Parameters
[in]TRANS
          TRANS is CHARACTER*1
          Specifies whether or not the transpose of A is used.
          = 'N':  No transpose, op(A) = A.
          = 'T':  Transpose, op(A) = A'.
[in]IRESID
          IRESID is INTEGER
          IRESID = 1 indicates zero-residual problem.
          IRESID = 2 indicates non-zero residual.
[in]M
          M is 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.
[in]N
          N is 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.
[in]NRHS
          NRHS is INTEGER
          The number of columns of the matrices X and B.
[in]A
          A is DOUBLE PRECISION array, dimension (LDA,N)
          The m-by-n matrix A.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A. LDA >= M.
[in]X
          X is DOUBLE PRECISION array, dimension (LDX,NRHS)
          If TRANS = 'N', the n-by-nrhs matrix X.
          If TRANS = 'T', the m-by-nrhs matrix X.
[in]LDX
          LDX is INTEGER
          The leading dimension of the array X.
          If TRANS = 'N', LDX >= N.
          If TRANS = 'T', LDX >= M.
[in]B
          B is DOUBLE PRECISION array, dimension (LDB,NRHS)
          If TRANS = 'N', the m-by-nrhs matrix B.
          If TRANS = 'T', the n-by-nrhs matrix B.
[in]LDB
          LDB is INTEGER
          The leading dimension of the array B.
          If TRANS = 'N', LDB >= M.
          If TRANS = 'T', LDB >= N.
[out]C
          C is DOUBLE PRECISION array, dimension (LDB,NRHS)
[out]WORK
          WORK is DOUBLE PRECISION array, dimension (LWORK)
[in]LWORK
          LWORK is INTEGER
          The length of the array WORK.  LWORK >= NRHS*(M+N).
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
November 2011

Definition at line 150 of file dqrt17.f.

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