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NAME DORGTR - generate a real orthogonal matrix Q which is defined as the product of n-1 elementary reflectors of order N, as returned by DSYTRD SYNOPSIS SUBROUTINE DORGTR( UPLO, N, A, LDA, TAU, WORK, LWORK, INFO ) CHARACTER UPLO INTEGER INFO, LDA, LWORK, N DOUBLE PRECISION A( LDA, * ), TAU( * ), WORK( LWORK ) PURPOSE DORGTR generates a real orthogonal matrix Q which is defined as the product of n-1 elementary reflectors of order N, as returned by DSYTRD: 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 reflectors from DSYTRD; = 'L': 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 N- by-N orthogonal matrix Q. LDA (input) INTEGER The leading dimension of the array A. LDA >= max(1,N). TAU (input) DOUBLE PRECISION array, dimension (N-1) TAU(i) must contain the scalar factor of the elemen- tary reflector H(i), as returned by DSYTRD. WORK (workspace) DOUBLE PRECISION 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. INFO (output) INTEGER = 0: successful exit < 0: if INFO = -i, the i-th argument had an illegal value