.TH DOPGTR 1 "November 2006" " LAPACK routine (version 3.1) " " LAPACK routine (version 3.1) " .SH 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 .SH SYNOPSIS .TP 19 SUBROUTINE DOPGTR( UPLO, N, AP, TAU, Q, LDQ, WORK, INFO ) .TP 19 .ti +4 CHARACTER UPLO .TP 19 .ti +4 INTEGER INFO, LDQ, N .TP 19 .ti +4 DOUBLE PRECISION AP( * ), Q( LDQ, * ), TAU( * ), WORK( * ) .SH 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 = \(aqU\(aq, Q = H(n-1) . . . H(2) H(1), .br if UPLO = \(aqL\(aq, Q = H(1) H(2) . . . H(n-1). .br .SH ARGUMENTS .TP 8 UPLO (input) CHARACTER*1 = \(aqU\(aq: Upper triangular packed storage used in previous call to DSPTRD; = \(aqL\(aq: Lower triangular packed storage used in previous call to DSPTRD. .TP 8 N (input) INTEGER The order of the matrix Q. N >= 0. .TP 8 AP (input) DOUBLE PRECISION array, dimension (N*(N+1)/2) The vectors which define the elementary reflectors, as returned by DSPTRD. .TP 8 TAU (input) DOUBLE PRECISION array, dimension (N-1) TAU(i) must contain the scalar factor of the elementary reflector H(i), as returned by DSPTRD. .TP 8 Q (output) DOUBLE PRECISION array, dimension (LDQ,N) The N-by-N orthogonal matrix Q. .TP 8 LDQ (input) INTEGER The leading dimension of the array Q. LDQ >= max(1,N). .TP 8 WORK (workspace) DOUBLE PRECISION array, dimension (N-1) .TP 8 INFO (output) INTEGER = 0: successful exit .br < 0: if INFO = -i, the i-th argument had an illegal value