LAPACK  3.5.0
LAPACK: Linear Algebra PACKage
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sqrt14.f File Reference

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Functions/Subroutines

real function sqrt14 (TRANS, M, N, NRHS, A, LDA, X, LDX, WORK, LWORK)
 SQRT14 More...
 

Function/Subroutine Documentation

real function sqrt14 ( character  TRANS,
integer  M,
integer  N,
integer  NRHS,
real, dimension( lda, * )  A,
integer  LDA,
real, dimension( ldx, * )  X,
integer  LDX,
real, dimension( lwork )  WORK,
integer  LWORK 
)

SQRT14

Purpose:
 SQRT14 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
[in]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'.
[in]M
          M is INTEGER
          The number of rows of the matrix A.
[in]N
          N is INTEGER
          The number of columns of the matrix A.
[in]NRHS
          NRHS is INTEGER
          The number of right hand sides, i.e., the number of columns
          of X.
[in]A
          A is REAL array, dimension (LDA,N)
          The M-by-N matrix A.
[in]LDA
          LDA is INTEGER
          The leading dimension of the array A.
[in]X
          X is REAL 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.
[out]WORK
          WORK is REAL array dimension (LWORK)
[in]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.
Date
November 2011

Definition at line 116 of file sqrt14.f.

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