NAME

       sgeqrt.f -

SYNOPSIS

   Functions/Subroutines
       subroutine sgeqrt (M, N, NB, A, LDA, T, LDT, WORK, INFO)
           SGEQRT

Function/Subroutine Documentation

   subroutine sgeqrt (integerM, integerN, integerNB, real, dimension( lda, * )A, integerLDA,
       real, dimension( ldt, * )T, integerLDT, real, dimension( * )WORK, integerINFO)
       SGEQRT

       Purpose:

            SGEQRT computes a blocked QR factorization of a real M-by-N matrix A
            using the compact WY representation of Q.

       Parameters:
           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.  N >= 0.

           NB

                     NB is INTEGER
                     The block size to be used in the blocked QR.  MIN(M,N) >= NB >= 1.

           A

                     A is REAL array, dimension (LDA,N)
                     On entry, the M-by-N matrix A.
                     On exit, the elements on and above the diagonal of the array
                     contain the min(M,N)-by-N upper trapezoidal matrix R (R is
                     upper triangular if M >= N); the elements below the diagonal
                     are the columns of V.

           LDA

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

           T

                     T is REAL array, dimension (LDT,MIN(M,N))
                     The upper triangular block reflectors stored in compact form
                     as a sequence of upper triangular blocks.  See below
                     for further details.

           LDT

                     LDT is INTEGER
                     The leading dimension of the array T.  LDT >= NB.

           WORK

                     WORK is REAL array, dimension (NB*N)

           INFO

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

       Author:
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Date:
           November 2013

       Further Details:

             The matrix V stores the elementary reflectors H(i) in the i-th column
             below the diagonal. For example, if M=5 and N=3, the matrix V is

                          V = (  1       )
                              ( v1  1    )
                              ( v1 v2  1 )
                              ( v1 v2 v3 )
                              ( v1 v2 v3 )

             where the vi's represent the vectors which define H(i), which are returned
             in the matrix A.  The 1's along the diagonal of V are not stored in A.

             Let K=MIN(M,N).  The number of blocks is B = ceiling(K/NB), where each
             block is of order NB except for the last block, which is of order
             IB = K - (B-1)*NB.  For each of the B blocks, a upper triangular block
             reflector factor is computed: T1, T2, ..., TB.  The NB-by-NB (and IB-by-IB
             for the last block) T's are stored in the NB-by-N matrix T as

                          T = (T1 T2 ... TB).

       Definition at line 142 of file sgeqrt.f.

Author

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