dqrt17.f - Man Page

double precision function dqrt17 (trans, iresid, m, n, nrhs, a, lda, x, ldx, b, ldb, c, work, lwork)
DQRT17

DQRT17

Purpose:

 DQRT17 computes the ratio

    norm(R**T * op(A)) / ( norm(A) * alpha * max(M,N,NRHS) * EPS ),

 where R = B - op(A)*X, op(A) is A or A**T, depending on TRANS, EPS
 is the machine epsilon, and

    alpha = norm(B) if IRESID = 1 (zero-residual problem)
    alpha = norm(R) if IRESID = 2 (otherwise).

 The norm used is the 1-norm.

Parameters

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**T.

IRESID

          IRESID is INTEGER
          IRESID = 1 indicates zero-residual problem.
          IRESID = 2 indicates non-zero residual.

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.

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.

NRHS

          NRHS is INTEGER
          The number of columns of the matrices X and B.

A

          A is DOUBLE PRECISION array, dimension (LDA,N)
          The m-by-n matrix A.

LDA

          LDA is INTEGER
          The leading dimension of the array A. LDA >= M.

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.

LDX

          LDX is INTEGER
          The leading dimension of the array X.
          If TRANS = 'N', LDX >= N.
          If TRANS = 'T', LDX >= M.

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.

LDB

          LDB is INTEGER
          The leading dimension of the array B.
          If TRANS = 'N', LDB >= M.
          If TRANS = 'T', LDB >= N.

C

          C is DOUBLE PRECISION array, dimension (LDB,NRHS)

WORK

          WORK is DOUBLE PRECISION array, dimension (LWORK)

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.

Definition at line 151 of file dqrt17.f.