SGELQ2(3)      LAPACK routine of NEC Numeric Library Collection      SGELQ2(3)



NAME
       SGELQ2

SYNOPSIS
       SUBROUTINE SGELQ2 (M, N, A, LDA, TAU, WORK, INFO)



PURPOSE
            SGELQ2 computes an LQ factorization of a real m by n matrix A:
            A = L * Q.




ARGUMENTS
           M         (input)
                     M is INTEGER
                     The number of rows of the matrix A.  M >= 0.

           N         (input)
                     N is INTEGER
                     The number of columns of the matrix A.  N >= 0.

           A         (input/output)
                     A is REAL array, dimension (LDA,N)
                     On entry, the m by n matrix A.
                     On exit, the elements on and below the diagonal of the array
                     contain the m by min(m,n) lower trapezoidal matrix L (L is
                     lower triangular if m <= n); the elements above the diagonal,
                     with the array TAU, represent the orthogonal matrix Q as a
                     product of elementary reflectors (see Further Details).

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

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

           WORK      (output)
                     WORK is REAL array, dimension (M)

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






FURTHER DETAILS
             The matrix Q is represented as a product of elementary reflectors

                Q = H(k) . . . H(2) H(1), 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:n) is stored on exit in A(i,i+1:n),
             and tau in TAU(i).



LAPACK routine                  31 October 2017                      SGELQ2(3)