LAPACK 3.3.0

zggrqf.f

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00001       SUBROUTINE ZGGRQF( M, P, N, A, LDA, TAUA, B, LDB, TAUB, WORK,
00002      $                   LWORK, INFO )
00003 *
00004 *  -- LAPACK routine (version 3.2) --
00005 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00006 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00007 *     November 2006
00008 *
00009 *     .. Scalar Arguments ..
00010       INTEGER            INFO, LDA, LDB, LWORK, M, N, P
00011 *     ..
00012 *     .. Array Arguments ..
00013       COMPLEX*16         A( LDA, * ), B( LDB, * ), TAUA( * ), TAUB( * ),
00014      $                   WORK( * )
00015 *     ..
00016 *
00017 *  Purpose
00018 *  =======
00019 *
00020 *  ZGGRQF computes a generalized RQ factorization of an M-by-N matrix A
00021 *  and a P-by-N matrix B:
00022 *
00023 *              A = R*Q,        B = Z*T*Q,
00024 *
00025 *  where Q is an N-by-N unitary matrix, Z is a P-by-P unitary
00026 *  matrix, and R and T assume one of the forms:
00027 *
00028 *  if M <= N,  R = ( 0  R12 ) M,   or if M > N,  R = ( R11 ) M-N,
00029 *                   N-M  M                           ( R21 ) N
00030 *                                                       N
00031 *
00032 *  where R12 or R21 is upper triangular, and
00033 *
00034 *  if P >= N,  T = ( T11 ) N  ,   or if P < N,  T = ( T11  T12 ) P,
00035 *                  (  0  ) P-N                         P   N-P
00036 *                     N
00037 *
00038 *  where T11 is upper triangular.
00039 *
00040 *  In particular, if B is square and nonsingular, the GRQ factorization
00041 *  of A and B implicitly gives the RQ factorization of A*inv(B):
00042 *
00043 *               A*inv(B) = (R*inv(T))*Z'
00044 *
00045 *  where inv(B) denotes the inverse of the matrix B, and Z' denotes the
00046 *  conjugate transpose of the matrix Z.
00047 *
00048 *  Arguments
00049 *  =========
00050 *
00051 *  M       (input) INTEGER
00052 *          The number of rows of the matrix A.  M >= 0.
00053 *
00054 *  P       (input) INTEGER
00055 *          The number of rows of the matrix B.  P >= 0.
00056 *
00057 *  N       (input) INTEGER
00058 *          The number of columns of the matrices A and B. N >= 0.
00059 *
00060 *  A       (input/output) COMPLEX*16 array, dimension (LDA,N)
00061 *          On entry, the M-by-N matrix A.
00062 *          On exit, if M <= N, the upper triangle of the subarray
00063 *          A(1:M,N-M+1:N) contains the M-by-M upper triangular matrix R;
00064 *          if M > N, the elements on and above the (M-N)-th subdiagonal
00065 *          contain the M-by-N upper trapezoidal matrix R; the remaining
00066 *          elements, with the array TAUA, represent the unitary
00067 *          matrix Q as a product of elementary reflectors (see Further
00068 *          Details).
00069 *
00070 *  LDA     (input) INTEGER
00071 *          The leading dimension of the array A. LDA >= max(1,M).
00072 *
00073 *  TAUA    (output) COMPLEX*16 array, dimension (min(M,N))
00074 *          The scalar factors of the elementary reflectors which
00075 *          represent the unitary matrix Q (see Further Details).
00076 *
00077 *  B       (input/output) COMPLEX*16 array, dimension (LDB,N)
00078 *          On entry, the P-by-N matrix B.
00079 *          On exit, the elements on and above the diagonal of the array
00080 *          contain the min(P,N)-by-N upper trapezoidal matrix T (T is
00081 *          upper triangular if P >= N); the elements below the diagonal,
00082 *          with the array TAUB, represent the unitary matrix Z as a
00083 *          product of elementary reflectors (see Further Details).
00084 *
00085 *  LDB     (input) INTEGER
00086 *          The leading dimension of the array B. LDB >= max(1,P).
00087 *
00088 *  TAUB    (output) COMPLEX*16 array, dimension (min(P,N))
00089 *          The scalar factors of the elementary reflectors which
00090 *          represent the unitary matrix Z (see Further Details).
00091 *
00092 *  WORK    (workspace/output) COMPLEX*16 array, dimension (MAX(1,LWORK))
00093 *          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
00094 *
00095 *  LWORK   (input) INTEGER
00096 *          The dimension of the array WORK. LWORK >= max(1,N,M,P).
00097 *          For optimum performance LWORK >= max(N,M,P)*max(NB1,NB2,NB3),
00098 *          where NB1 is the optimal blocksize for the RQ factorization
00099 *          of an M-by-N matrix, NB2 is the optimal blocksize for the
00100 *          QR factorization of a P-by-N matrix, and NB3 is the optimal
00101 *          blocksize for a call of ZUNMRQ.
00102 *
00103 *          If LWORK = -1, then a workspace query is assumed; the routine
00104 *          only calculates the optimal size of the WORK array, returns
00105 *          this value as the first entry of the WORK array, and no error
00106 *          message related to LWORK is issued by XERBLA.
00107 *
00108 *  INFO    (output) INTEGER
00109 *          = 0:  successful exit
00110 *          < 0:  if INFO=-i, the i-th argument had an illegal value.
00111 *
00112 *  Further Details
00113 *  ===============
00114 *
00115 *  The matrix Q is represented as a product of elementary reflectors
00116 *
00117 *     Q = H(1) H(2) . . . H(k), where k = min(m,n).
00118 *
00119 *  Each H(i) has the form
00120 *
00121 *     H(i) = I - taua * v * v'
00122 *
00123 *  where taua is a complex scalar, and v is a complex vector with
00124 *  v(n-k+i+1:n) = 0 and v(n-k+i) = 1; v(1:n-k+i-1) is stored on exit in
00125 *  A(m-k+i,1:n-k+i-1), and taua in TAUA(i).
00126 *  To form Q explicitly, use LAPACK subroutine ZUNGRQ.
00127 *  To use Q to update another matrix, use LAPACK subroutine ZUNMRQ.
00128 *
00129 *  The matrix Z is represented as a product of elementary reflectors
00130 *
00131 *     Z = H(1) H(2) . . . H(k), where k = min(p,n).
00132 *
00133 *  Each H(i) has the form
00134 *
00135 *     H(i) = I - taub * v * v'
00136 *
00137 *  where taub is a complex scalar, and v is a complex vector with
00138 *  v(1:i-1) = 0 and v(i) = 1; v(i+1:p) is stored on exit in B(i+1:p,i),
00139 *  and taub in TAUB(i).
00140 *  To form Z explicitly, use LAPACK subroutine ZUNGQR.
00141 *  To use Z to update another matrix, use LAPACK subroutine ZUNMQR.
00142 *
00143 *  =====================================================================
00144 *
00145 *     .. Local Scalars ..
00146       LOGICAL            LQUERY
00147       INTEGER            LOPT, LWKOPT, NB, NB1, NB2, NB3
00148 *     ..
00149 *     .. External Subroutines ..
00150       EXTERNAL           XERBLA, ZGEQRF, ZGERQF, ZUNMRQ
00151 *     ..
00152 *     .. External Functions ..
00153       INTEGER            ILAENV
00154       EXTERNAL           ILAENV
00155 *     ..
00156 *     .. Intrinsic Functions ..
00157       INTRINSIC          INT, MAX, MIN
00158 *     ..
00159 *     .. Executable Statements ..
00160 *
00161 *     Test the input parameters
00162 *
00163       INFO = 0
00164       NB1 = ILAENV( 1, 'ZGERQF', ' ', M, N, -1, -1 )
00165       NB2 = ILAENV( 1, 'ZGEQRF', ' ', P, N, -1, -1 )
00166       NB3 = ILAENV( 1, 'ZUNMRQ', ' ', M, N, P, -1 )
00167       NB = MAX( NB1, NB2, NB3 )
00168       LWKOPT = MAX( N, M, P )*NB
00169       WORK( 1 ) = LWKOPT
00170       LQUERY = ( LWORK.EQ.-1 )
00171       IF( M.LT.0 ) THEN
00172          INFO = -1
00173       ELSE IF( P.LT.0 ) THEN
00174          INFO = -2
00175       ELSE IF( N.LT.0 ) THEN
00176          INFO = -3
00177       ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
00178          INFO = -5
00179       ELSE IF( LDB.LT.MAX( 1, P ) ) THEN
00180          INFO = -8
00181       ELSE IF( LWORK.LT.MAX( 1, M, P, N ) .AND. .NOT.LQUERY ) THEN
00182          INFO = -11
00183       END IF
00184       IF( INFO.NE.0 ) THEN
00185          CALL XERBLA( 'ZGGRQF', -INFO )
00186          RETURN
00187       ELSE IF( LQUERY ) THEN
00188          RETURN
00189       END IF
00190 *
00191 *     RQ factorization of M-by-N matrix A: A = R*Q
00192 *
00193       CALL ZGERQF( M, N, A, LDA, TAUA, WORK, LWORK, INFO )
00194       LOPT = WORK( 1 )
00195 *
00196 *     Update B := B*Q'
00197 *
00198       CALL ZUNMRQ( 'Right', 'Conjugate Transpose', P, N, MIN( M, N ),
00199      $             A( MAX( 1, M-N+1 ), 1 ), LDA, TAUA, B, LDB, WORK,
00200      $             LWORK, INFO )
00201       LOPT = MAX( LOPT, INT( WORK( 1 ) ) )
00202 *
00203 *     QR factorization of P-by-N matrix B: B = Z*T
00204 *
00205       CALL ZGEQRF( P, N, B, LDB, TAUB, WORK, LWORK, INFO )
00206       WORK( 1 ) = MAX( LOPT, INT( WORK( 1 ) ) )
00207 *
00208       RETURN
00209 *
00210 *     End of ZGGRQF
00211 *
00212       END
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