dbdt01.f - Man Page

subroutine dbdt01 (m, n, kd, a, lda, q, ldq, d, e, pt, ldpt, work, resid)
DBDT01

DBDT01

Purpose:

 DBDT01 reconstructs a general matrix A from its bidiagonal form
    A = Q * B * P**T
 where Q (m by min(m,n)) and P**T (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 * P**T) / ( n * norm(A) * EPS )
 where EPS is the machine precision.

Parameters

M

          M is INTEGER
          The number of rows of the matrices A and Q.

N

          N is INTEGER
          The number of columns of the matrices A and P**T.

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.

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 >= max(1,M).

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**T.

LDQ

          LDQ is INTEGER
          The leading dimension of the array Q.  LDQ >= max(1,M).

D

          D is DOUBLE PRECISION array, dimension (min(M,N))
          The diagonal elements of the bidiagonal matrix B.

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.

PT

          PT is DOUBLE PRECISION array, dimension (LDPT,N)
          The min(m,n) by n orthogonal matrix P**T in the reduction
          A = Q * B * P**T.

LDPT

          LDPT is INTEGER
          The leading dimension of the array PT.
          LDPT >= max(1,min(M,N)).

WORK

          WORK is DOUBLE PRECISION array, dimension (M+N)

RESID

          RESID is DOUBLE PRECISION
          The test ratio:
          norm(A - Q * B * P**T) / ( n * norm(A) * EPS )

Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 139 of file dbdt01.f.