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dbdt01.f File Reference

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Functions/Subroutines

subroutine dbdt01 (M, N, KD, A, LDA, Q, LDQ, D, E, PT, LDPT, WORK, RESID)
 DBDT01 More...
 

Function/Subroutine Documentation

subroutine dbdt01 ( integer  M,
integer  N,
integer  KD,
double precision, dimension( lda, * )  A,
integer  LDA,
double precision, dimension( ldq, * )  Q,
integer  LDQ,
double precision, dimension( * )  D,
double precision, dimension( * )  E,
double precision, dimension( ldpt, * )  PT,
integer  LDPT,
double precision, dimension( * )  WORK,
double precision  RESID 
)

DBDT01

Purpose:
 DBDT01 reconstructs a general matrix A from its bidiagonal form
    A = Q * B * P'
 where Q (m by min(m,n)) and P' (min(m,n) by n) are orthogonal
 matrices and B is bidiagonal.

 The test ratio to test the reduction is
    RESID = norm( A - Q * B * PT ) / ( n * norm(A) * EPS )
 where PT = P' and EPS is the machine precision.
Parameters
[in]M
          M is INTEGER
          The number of rows of the matrices A and Q.
[in]N
          N is INTEGER
          The number of columns of the matrices A and P'.
[in]KD
          KD is INTEGER
          If KD = 0, B is diagonal and the array E is not referenced.
          If KD = 1, the reduction was performed by xGEBRD; B is upper
          bidiagonal if M >= N, and lower bidiagonal if M < N.
          If KD = -1, the reduction was performed by xGBBRD; B is
          always upper bidiagonal.
[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 >= max(1,M).
[in]Q
          Q is DOUBLE PRECISION array, dimension (LDQ,N)
          The m by min(m,n) orthogonal matrix Q in the reduction
          A = Q * B * P'.
[in]LDQ
          LDQ is INTEGER
          The leading dimension of the array Q.  LDQ >= max(1,M).
[in]D
          D is DOUBLE PRECISION array, dimension (min(M,N))
          The diagonal elements of the bidiagonal matrix B.
[in]E
          E is DOUBLE PRECISION array, dimension (min(M,N)-1)
          The superdiagonal elements of the bidiagonal matrix B if
          m >= n, or the subdiagonal elements of B if m < n.
[in]PT
          PT is DOUBLE PRECISION array, dimension (LDPT,N)
          The min(m,n) by n orthogonal matrix P' in the reduction
          A = Q * B * P'.
[in]LDPT
          LDPT is INTEGER
          The leading dimension of the array PT.
          LDPT >= max(1,min(M,N)).
[out]WORK
          WORK is DOUBLE PRECISION array, dimension (M+N)
[out]RESID
          RESID is DOUBLE PRECISION
          The test ratio:  norm(A - Q * B * P') / ( n * norm(A) * EPS )
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
November 2011

Definition at line 140 of file dbdt01.f.

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