sorgtr(3)

NAME

SORGTR - generate a real orthogonal matrix Q which is de

fined as the product of n-1 elementary reflectors of order N, as

returned by SSYTRD

SYNOPSIS

SUBROUTINE SORGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO
)
    CHARACTER      UPLO
    INTEGER        INFO, LDA, LWORK, N
    REAL           A( LDA, * ), TAU( * ), WORK( * )

PURPOSE

SORGTR generates a real orthogonal matrix Q which is de

fined as the product of n-1 elementary reflectors of order N, as

returned by SSYTRD: 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 triangle of A contains elementary re

flectors from SSYTRD; = 'L': Lower triangle of A contains elemen

tary reflectors from SSYTRD.

N (input) INTEGER

The order of the matrix Q. N >= 0.

A (input/output) REAL array, dimension (LDA,N)

On entry, the vectors which define the elementary

reflectors, as returned by SSYTRD. On exit, the N-by-N orthogo

nal matrix Q.

LDA (input) INTEGER

The leading dimension of the array A. LDA >=

max(1,N).

TAU (input) REAL array, dimension (N-1)

TAU(i) must contain the scalar factor of the ele

mentary reflector H(i), as returned by SSYTRD.

WORK (workspace/output) REAL array, dimension (LWORK)

On exit, if INFO = 0, WORK(1) returns the optimal

LWORK.

LWORK (input) INTEGER

The dimension of the array WORK. LWORK >=

max(1,N-1). For optimum performance LWORK >= (N-1)*NB, where NB

is the optimal blocksize.

If LWORK = -1, then a workspace query is assumed;

the routine only calculates the optimal size of the WORK array,

returns this value as the first entry of the WORK array, and no

error message related to LWORK is issued by XERBLA.

INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille

gal value

LAPACK version 3.0 15 June 2000

SORGTR(3)