DORGQR generates an M-by-N real matrix Q with orthonormal columns,


 which is defined as the first N columns of a product of K elementary


 reflectors of order M


       Q  =  H(1) H(2) . . . H(k)


 as returned by DGEQRF.

M

          M is INTEGER


          The number of rows of the matrix Q. M >= 0.

N

          N is INTEGER


          The number of columns of the matrix Q. M >= N >= 0.

K

          K is INTEGER


          The number of elementary reflectors whose product defines the


          matrix Q. N >= K >= 0.

A

          A is DOUBLE PRECISION array, dimension (LDA,N)


          On entry, the i-th column must contain the vector which


          defines the elementary reflector H(i), for i = 1,2,...,k, as


          returned by DGEQRF in the first k columns of its array


          argument A.


          On exit, the M-by-N matrix Q.

LDA

          LDA is INTEGER


          The first dimension of the array A. LDA >= max(1,M).

TAU

          TAU is DOUBLE PRECISION array, dimension (K)


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


          reflector H(i), as returned by DGEQRF.

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).


          For optimum performance LWORK >= N*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 has an illegal value

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

December 2016