Solve the least squares problem


     min || A*X - B ||


 using the QR factorization


     A = Q*R


 computed by DGEQRF.

M

          M is INTEGER


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

N

          N is INTEGER


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

NRHS

          NRHS is INTEGER


          The number of columns of B.  NRHS >= 0.

A

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


          Details of the QR factorization of the original matrix A as


          returned by DGEQRF.

LDA

          LDA is INTEGER


          The leading dimension of the array A.  LDA >= M.

TAU

          TAU is DOUBLE PRECISION array, dimension (N)


          Details of the orthogonal matrix Q.

B

          B is DOUBLE PRECISION array, dimension (LDB,NRHS)


          On entry, the m-by-nrhs right hand side matrix B.


          On exit, the n-by-nrhs solution matrix X.

LDB

          LDB is INTEGER


          The leading dimension of the array B. LDB >= M.

WORK

          WORK is DOUBLE PRECISION array, dimension (LWORK)

LWORK

          LWORK is INTEGER


          The length of the array WORK.  LWORK must be at least NRHS,


          and should be at least NRHS*NB, where NB is the block size


          for this environment.

INFO

          INFO is INTEGER


          = 0: successful exit


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

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