


DOPGTR(3f)         LAPACK routine (version 3.1)        DOPGTR(3f)


NAME
       DOPGTR  - a real orthogonal matrix Q which is defined as the product of
       n-1 elementary reflectors H(i) of order n, as returned by DSPTRD  using
       packed storage

SYNOPSIS
       SUBROUTINE DOPGTR( UPLO, N, AP, TAU, Q, LDQ, WORK, INFO )

           CHARACTER      UPLO

           INTEGER        INFO, LDQ, N

           DOUBLE         PRECISION AP( * ), Q( LDQ, * ), TAU( * ), WORK( * )

PURPOSE
       DOPGTR  generates  a  real  orthogonal matrix Q which is defined as the
       product of n-1 elementary reflectors H(i) of order n,  as  returned  by
       DSPTRD using packed storage:

       if UPLO = 'U', Q = H(n-1) . . . H(2) H(1),

       if UPLO = 'L', Q = H(1) H(2) . . . H(n-1).


ARGUMENTS
       UPLO    (input) CHARACTER*1
               = 'U': Upper triangular packed storage used in previous call to
               DSPTRD; = 'L': Lower triangular packed storage used in previous
               call to DSPTRD.

       N       (input) INTEGER
               The order of the matrix Q. N >= 0.

       AP      (input) DOUBLE PRECISION array, dimension (N*(N+1)/2)
               The vectors which define the elementary reflectors, as returned
               by DSPTRD.

       TAU     (input) DOUBLE PRECISION array, dimension (N-1)
               TAU(i) must contain the scalar factor of the elementary reflec-
               tor H(i), as returned by DSPTRD.

       Q       (output) DOUBLE PRECISION array, dimension (LDQ,N)
               The N-by-N orthogonal matrix Q.

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

       WORK    (workspace) DOUBLE PRECISION array, dimension (N-1)

       INFO    (output) INTEGER
               = 0:  successful exit
               < 0:  if INFO = -i, the i-th argument had an illegal value





 LAPACK routine (version 3November 2006                         1


