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).

UPLO

          UPLO is CHARACTER*1


          = 'U': Upper triangle of A contains elementary reflectors


                 from DSYTRD;


          = 'L': Lower triangle of A contains elementary reflectors


                 from DSYTRD.

N

          N is INTEGER


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

A

          A is 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

          LDA is INTEGER


          The leading dimension of the array A. LDA >= max(1,N).

TAU

          TAU is DOUBLE PRECISION array, dimension (N-1)


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


          reflector H(i), as returned by DSYTRD.

WORK

          WORK is DOUBLE PRECISION array, dimension (MAX(1,LWORK))


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

LWORK

          LWORK is 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

          INFO is INTEGER


          = 0:  successful exit


          < 0:  if INFO = -i, the i-th argument had an illegal value

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NAG Ltd.

November 2011