dorgtr (l)  Linux Manuals
dorgtr: generates a real orthogonal matrix Q which is defined as the product of n1 elementary reflectors of order N, as returned by DSYTRD
NAME
DORGTR  generates a real orthogonal matrix Q which is defined as the product of n1 elementary reflectors of order N, as returned by DSYTRDSYNOPSIS
 SUBROUTINE DORGTR(
 UPLO, N, A, LDA, TAU, WORK, LWORK, INFO )
 CHARACTER UPLO
 INTEGER INFO, LDA, LWORK, N
 DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( * )
PURPOSE
DORGTR generates a real orthogonal matrix Q which is defined as the product of n1 elementary reflectors of order N, as returned by DSYTRD: if UPLO = aqUaq, Q = H(n1) . . . H(2) H(1),if UPLO = aqLaq, Q = H(1) H(2) . . . H(n1).
ARGUMENTS
 UPLO (input) CHARACTER*1
 = aqUaq: Upper triangle of A contains elementary reflectors from DSYTRD; = aqLaq: Lower triangle of A contains elementary reflectors from DSYTRD.
 N (input) INTEGER
 The order of the matrix Q. N >= 0.
 A (input/output) DOUBLE PRECISION array, dimension (LDA,N)
 On entry, the vectors which define the elementary reflectors, as returned by DSYTRD. On exit, the NbyN orthogonal matrix Q.
 LDA (input) INTEGER
 The leading dimension of the array A. LDA >= max(1,N).
 TAU (input) DOUBLE PRECISION array, dimension (N1)
 TAU(i) must contain the scalar factor of the elementary reflector H(i), as returned by DSYTRD.
 WORK (workspace/output) DOUBLE PRECISION array, dimension (MAX(1,LWORK))
 On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
 LWORK (input) INTEGER
 The dimension of the array WORK. LWORK >= max(1,N1). For optimum performance LWORK >= (N1)*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 ith argument had an illegal value