Return to zung2l.f CVS log

Up to [local] / rpl / lapack / lapack

Cohérence

    1: *> \brief \b ZUNG2L
    2: *
    3: *  =========== DOCUMENTATION ===========
    4: *
    5: * Online html documentation available at 
    6: *            http://www.netlib.org/lapack/explore-html/ 
    7: *
    8: *> \htmlonly
    9: *> Download ZUNG2L + dependencies 
   10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/zung2l.f"> 
   11: *> [TGZ]</a> 
   12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/zung2l.f"> 
   13: *> [ZIP]</a> 
   14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/zung2l.f"> 
   15: *> [TXT]</a>
   16: *> \endhtmlonly 
   17: *
   18: *  Definition:
   19: *  ===========
   20: *
   21: *       SUBROUTINE ZUNG2L( M, N, K, A, LDA, TAU, WORK, INFO )
   22: * 
   23: *       .. Scalar Arguments ..
   24: *       INTEGER            INFO, K, LDA, M, N
   25: *       ..
   26: *       .. Array Arguments ..
   27: *       COMPLEX*16         A( LDA, * ), TAU( * ), WORK( * )
   28: *       ..
   29: *  
   30: *
   31: *> \par Purpose:
   32: *  =============
   33: *>
   34: *> \verbatim
   35: *>
   36: *> ZUNG2L generates an m by n complex matrix Q with orthonormal columns,
   37: *> which is defined as the last n columns of a product of k elementary
   38: *> reflectors of order m
   39: *>
   40: *>       Q  =  H(k) . . . H(2) H(1)
   41: *>
   42: *> as returned by ZGEQLF.
   43: *> \endverbatim
   44: *
   45: *  Arguments:
   46: *  ==========
   47: *
   48: *> \param[in] M
   49: *> \verbatim
   50: *>          M is INTEGER
   51: *>          The number of rows of the matrix Q. M >= 0.
   52: *> \endverbatim
   53: *>
   54: *> \param[in] N
   55: *> \verbatim
   56: *>          N is INTEGER
   57: *>          The number of columns of the matrix Q. M >= N >= 0.
   58: *> \endverbatim
   59: *>
   60: *> \param[in] K
   61: *> \verbatim
   62: *>          K is INTEGER
   63: *>          The number of elementary reflectors whose product defines the
   64: *>          matrix Q. N >= K >= 0.
   65: *> \endverbatim
   66: *>
   67: *> \param[in,out] A
   68: *> \verbatim
   69: *>          A is COMPLEX*16 array, dimension (LDA,N)
   70: *>          On entry, the (n-k+i)-th column must contain the vector which
   71: *>          defines the elementary reflector H(i), for i = 1,2,...,k, as
   72: *>          returned by ZGEQLF in the last k columns of its array
   73: *>          argument A.
   74: *>          On exit, the m-by-n matrix Q.
   75: *> \endverbatim
   76: *>
   77: *> \param[in] LDA
   78: *> \verbatim
   79: *>          LDA is INTEGER
   80: *>          The first dimension of the array A. LDA >= max(1,M).
   81: *> \endverbatim
   82: *>
   83: *> \param[in] TAU
   84: *> \verbatim
   85: *>          TAU is COMPLEX*16 array, dimension (K)
   86: *>          TAU(i) must contain the scalar factor of the elementary
   87: *>          reflector H(i), as returned by ZGEQLF.
   88: *> \endverbatim
   89: *>
   90: *> \param[out] WORK
   91: *> \verbatim
   92: *>          WORK is COMPLEX*16 array, dimension (N)
   93: *> \endverbatim
   94: *>
   95: *> \param[out] INFO
   96: *> \verbatim
   97: *>          INFO is INTEGER
   98: *>          = 0: successful exit
   99: *>          < 0: if INFO = -i, the i-th argument has an illegal value
  100: *> \endverbatim
  101: *
  102: *  Authors:
  103: *  ========
  104: *
  105: *> \author Univ. of Tennessee 
  106: *> \author Univ. of California Berkeley 
  107: *> \author Univ. of Colorado Denver 
  108: *> \author NAG Ltd. 
  109: *
  110: *> \date November 2011
  111: *
  112: *> \ingroup complex16OTHERcomputational
  113: *
  114: *  =====================================================================
  115:       SUBROUTINE ZUNG2L( M, N, K, A, LDA, TAU, WORK, INFO )
  116: *
  117: *  -- LAPACK computational routine (version 3.4.0) --
  118: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
  119: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
  120: *     November 2011
  121: *
  122: *     .. Scalar Arguments ..
  123:       INTEGER            INFO, K, LDA, M, N
  124: *     ..
  125: *     .. Array Arguments ..
  126:       COMPLEX*16         A( LDA, * ), TAU( * ), WORK( * )
  127: *     ..
  128: *
  129: *  =====================================================================
  130: *
  131: *     .. Parameters ..
  132:       COMPLEX*16         ONE, ZERO
  133:       PARAMETER          ( ONE = ( 1.0D+0, 0.0D+0 ),
  134:      $                   ZERO = ( 0.0D+0, 0.0D+0 ) )
  135: *     ..
  136: *     .. Local Scalars ..
  137:       INTEGER            I, II, J, L
  138: *     ..
  139: *     .. External Subroutines ..
  140:       EXTERNAL           XERBLA, ZLARF, ZSCAL
  141: *     ..
  142: *     .. Intrinsic Functions ..
  143:       INTRINSIC          MAX
  144: *     ..
  145: *     .. Executable Statements ..
  146: *
  147: *     Test the input arguments
  148: *
  149:       INFO = 0
  150:       IF( M.LT.0 ) THEN
  151:          INFO = -1
  152:       ELSE IF( N.LT.0 .OR. N.GT.M ) THEN
  153:          INFO = -2
  154:       ELSE IF( K.LT.0 .OR. K.GT.N ) THEN
  155:          INFO = -3
  156:       ELSE IF( LDA.LT.MAX( 1, M ) ) THEN
  157:          INFO = -5
  158:       END IF
  159:       IF( INFO.NE.0 ) THEN
  160:          CALL XERBLA( 'ZUNG2L', -INFO )
  161:          RETURN
  162:       END IF
  163: *
  164: *     Quick return if possible
  165: *
  166:       IF( N.LE.0 )
  167:      $   RETURN
  168: *
  169: *     Initialise columns 1:n-k to columns of the unit matrix
  170: *
  171:       DO 20 J = 1, N - K
  172:          DO 10 L = 1, M
  173:             A( L, J ) = ZERO
  174:    10    CONTINUE
  175:          A( M-N+J, J ) = ONE
  176:    20 CONTINUE
  177: *
  178:       DO 40 I = 1, K
  179:          II = N - K + I
  180: *
  181: *        Apply H(i) to A(1:m-k+i,1:n-k+i) from the left
  182: *
  183:          A( M-N+II, II ) = ONE
  184:          CALL ZLARF( 'Left', M-N+II, II-1, A( 1, II ), 1, TAU( I ), A,
  185:      $               LDA, WORK )
  186:          CALL ZSCAL( M-N+II-1, -TAU( I ), A( 1, II ), 1 )
  187:          A( M-N+II, II ) = ONE - TAU( I )
  188: *
  189: *        Set A(m-k+i+1:m,n-k+i) to zero
  190: *
  191:          DO 30 L = M - N + II + 1, M
  192:             A( L, II ) = ZERO
  193:    30    CONTINUE
  194:    40 CONTINUE
  195:       RETURN
  196: *
  197: *     End of ZUNG2L
  198: *
  199:       END