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NAME
     zgerq2 - compute an RQ factorization of a  complex  m  by  n
     matrix A

SYNOPSIS
     SUBROUTINE ZGERQ2( M, N, A, LDA, TAU, WORK, INFO )

     INTEGER INFO, LDA, M, N

     COMPLEX*16 A( LDA, * ), TAU( * ), WORK( * )



     #include <sunperf.h>

     void zgerq2(int m, int n, doublecomplex *za, int lda,  doub-
               lecomplex *tau, int *info) ;

PURPOSE
     ZGERQ2 computes an RQ factorization of  a  complex  m  by  n
     matrix A:  A = R * Q.


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

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

     A         (input/output) COMPLEX*16 array, dimension (LDA,N)
               On entry, the m by n matrix A.  On exit, if  m  <=
               n,  the  upper  triangle  of the subarray A(1:m,n-
               m+1:n) contains the m by m upper triangular matrix
               R;  if  m  >= n, the elements on and above the (m-
               n)-th subdiagonal contain the m by  n  upper  tra-
               pezoidal  matrix  R;  the remaining elements, with
               the array TAU, represent the unitary matrix Q as a
               product  of  elementary  reflectors  (see  Further
               Details).

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

     TAU       (output) COMPLEX*16 array, dimension (min(M,N))
               The scalar factors of  the  elementary  reflectors
               (see Further Details).

     WORK      (workspace) COMPLEX*16 array, dimension (M)

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

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'

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

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