dqrt14.f - Man Page

double precision function dqrt14 (trans, m, n, nrhs, a, lda, x, ldx, work, lwork)
DQRT14

DQRT14

Purpose:

 DQRT14 checks whether X is in the row space of A or A'.  It does so
 by scaling both X and A such that their norms are in the range
 [sqrt(eps), 1/sqrt(eps)], then computing a QR factorization of [A,X]
 (if TRANS = 'T') or an LQ factorization of [A',X]' (if TRANS = 'N'),
 and returning the norm of the trailing triangle, scaled by
 MAX(M,N,NRHS)*eps.

Parameters

TRANS

          TRANS is CHARACTER*1
          = 'N':  No transpose, check for X in the row space of A
          = 'T':  Transpose, check for X in the row space of A'.

M

          M is INTEGER
          The number of rows of the matrix A.

N

          N is INTEGER
          The number of columns of the matrix A.

NRHS

          NRHS is INTEGER
          The number of right hand sides, i.e., the number of columns
          of X.

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.

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.

WORK

          WORK is DOUBLE PRECISION array dimension (LWORK)

LWORK

          LWORK is INTEGER
          length of workspace array required
          If TRANS = 'N', LWORK >= (M+NRHS)*(N+2);
          if TRANS = 'T', LWORK >= (N+NRHS)*(M+2).

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 114 of file dqrt14.f.