SRC/dgeqr2p.f(3)           Library Functions Manual           SRC/dgeqr2p.f(3)

NAME
       SRC/dgeqr2p.f

SYNOPSIS
   Functions/Subroutines
       subroutine dgeqr2p (m, n, a, lda, tau, work, info)
           DGEQR2P computes the QR factorization of a general rectangular
           matrix with non-negative diagonal elements using an unblocked
           algorithm.

Function/Subroutine Documentation
   subroutine dgeqr2p (integer m, integer n, double precision, dimension( lda,
       * ) a, integer lda, double precision, dimension( * ) tau, double
       precision, dimension( * ) work, integer info)
       DGEQR2P computes the QR factorization of a general rectangular matrix
       with non-negative diagonal elements using an unblocked algorithm.

       Purpose:


            DGEQR2P computes a QR factorization of a real m-by-n matrix A:

               A = Q * ( R ),
                       ( 0 )

            where:

               Q is a m-by-m orthogonal matrix;
               R is an upper-triangular n-by-n matrix with nonnegative diagonal
               entries;
               0 is a (m-n)-by-n zero matrix, if m > n.

       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.

           A

                     A is DOUBLE PRECISION 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 diagonal entries of R are
                     nonnegative; the elements below the diagonal,
                     with the array TAU, represent the orthogonal matrix Q as a
                     product of elementary reflectors (see Further Details).

           LDA

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

           TAU

                     TAU is DOUBLE PRECISION array, dimension (min(M,N))
                     The scalar factors of the elementary reflectors (see Further
                     Details).

           WORK

                     WORK is DOUBLE PRECISION array, dimension (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.

       Further Details:


             The matrix Q is represented as a product of elementary reflectors

                Q = H(1) H(2) . . . H(k), where k = min(m,n).

             Each H(i) has the form

                H(i) = I - tau * v * v**T

             where tau is a real scalar, and v is a real vector with
             v(1:i-1) = 0 and v(i) = 1; v(i+1:m) is stored on exit in A(i+1:m,i),
             and tau in TAU(i).

            See Lapack Working Note 203 for details

       Definition at line 133 of file dgeqr2p.f.

Author
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LAPACK                          Version 3.12.0                SRC/dgeqr2p.f(3)