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    1: *> \brief \b ZLAQSP scales a symmetric/Hermitian matrix in packed storage, using scaling factors computed by sppequ.
    2: *
    3: *  =========== DOCUMENTATION ===========
    4: *
    5: * Online html documentation available at
    6: *            http://www.netlib.org/lapack/explore-html/
    7: *
    8: *> \htmlonly
    9: *> Download ZLAQSP + dependencies
   10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/zlaqsp.f">
   11: *> [TGZ]</a>
   12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/zlaqsp.f">
   13: *> [ZIP]</a>
   14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/zlaqsp.f">
   15: *> [TXT]</a>
   16: *> \endhtmlonly
   17: *
   18: *  Definition:
   19: *  ===========
   20: *
   21: *       SUBROUTINE ZLAQSP( UPLO, N, AP, S, SCOND, AMAX, EQUED )
   22: *
   23: *       .. Scalar Arguments ..
   24: *       CHARACTER          EQUED, UPLO
   25: *       INTEGER            N
   26: *       DOUBLE PRECISION   AMAX, SCOND
   27: *       ..
   28: *       .. Array Arguments ..
   29: *       DOUBLE PRECISION   S( * )
   30: *       COMPLEX*16         AP( * )
   31: *       ..
   32: *
   33: *
   34: *> \par Purpose:
   35: *  =============
   36: *>
   37: *> \verbatim
   38: *>
   39: *> ZLAQSP equilibrates a symmetric matrix A using the scaling factors
   40: *> in the vector S.
   41: *> \endverbatim
   42: *
   43: *  Arguments:
   44: *  ==========
   45: *
   46: *> \param[in] UPLO
   47: *> \verbatim
   48: *>          UPLO is CHARACTER*1
   49: *>          Specifies whether the upper or lower triangular part of the
   50: *>          symmetric matrix A is stored.
   51: *>          = 'U':  Upper triangular
   52: *>          = 'L':  Lower triangular
   53: *> \endverbatim
   54: *>
   55: *> \param[in] N
   56: *> \verbatim
   57: *>          N is INTEGER
   58: *>          The order of the matrix A.  N >= 0.
   59: *> \endverbatim
   60: *>
   61: *> \param[in,out] AP
   62: *> \verbatim
   63: *>          AP is COMPLEX*16 array, dimension (N*(N+1)/2)
   64: *>          On entry, the upper or lower triangle of the symmetric matrix
   65: *>          A, packed columnwise in a linear array.  The j-th column of A
   66: *>          is stored in the array AP as follows:
   67: *>          if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j;
   68: *>          if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = A(i,j) for j<=i<=n.
   69: *>
   70: *>          On exit, the equilibrated matrix:  diag(S) * A * diag(S), in
   71: *>          the same storage format as A.
   72: *> \endverbatim
   73: *>
   74: *> \param[in] S
   75: *> \verbatim
   76: *>          S is DOUBLE PRECISION array, dimension (N)
   77: *>          The scale factors for A.
   78: *> \endverbatim
   79: *>
   80: *> \param[in] SCOND
   81: *> \verbatim
   82: *>          SCOND is DOUBLE PRECISION
   83: *>          Ratio of the smallest S(i) to the largest S(i).
   84: *> \endverbatim
   85: *>
   86: *> \param[in] AMAX
   87: *> \verbatim
   88: *>          AMAX is DOUBLE PRECISION
   89: *>          Absolute value of largest matrix entry.
   90: *> \endverbatim
   91: *>
   92: *> \param[out] EQUED
   93: *> \verbatim
   94: *>          EQUED is CHARACTER*1
   95: *>          Specifies whether or not equilibration was done.
   96: *>          = 'N':  No equilibration.
   97: *>          = 'Y':  Equilibration was done, i.e., A has been replaced by
   98: *>                  diag(S) * A * diag(S).
   99: *> \endverbatim
  100: *
  101: *> \par Internal Parameters:
  102: *  =========================
  103: *>
  104: *> \verbatim
  105: *>  THRESH is a threshold value used to decide if scaling should be done
  106: *>  based on the ratio of the scaling factors.  If SCOND < THRESH,
  107: *>  scaling is done.
  108: *>
  109: *>  LARGE and SMALL are threshold values used to decide if scaling should
  110: *>  be done based on the absolute size of the largest matrix element.
  111: *>  If AMAX > LARGE or AMAX < SMALL, scaling is done.
  112: *> \endverbatim
  113: *
  114: *  Authors:
  115: *  ========
  116: *
  117: *> \author Univ. of Tennessee
  118: *> \author Univ. of California Berkeley
  119: *> \author Univ. of Colorado Denver
  120: *> \author NAG Ltd.
  121: *
  122: *> \ingroup complex16OTHERauxiliary
  123: *
  124: *  =====================================================================
  125:       SUBROUTINE ZLAQSP( UPLO, N, AP, S, SCOND, AMAX, EQUED )
  126: *
  127: *  -- LAPACK auxiliary routine --
  128: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
  129: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
  130: *
  131: *     .. Scalar Arguments ..
  132:       CHARACTER          EQUED, UPLO
  133:       INTEGER            N
  134:       DOUBLE PRECISION   AMAX, SCOND
  135: *     ..
  136: *     .. Array Arguments ..
  137:       DOUBLE PRECISION   S( * )
  138:       COMPLEX*16         AP( * )
  139: *     ..
  140: *
  141: *  =====================================================================
  142: *
  143: *     .. Parameters ..
  144:       DOUBLE PRECISION   ONE, THRESH
  145:       PARAMETER          ( ONE = 1.0D+0, THRESH = 0.1D+0 )
  146: *     ..
  147: *     .. Local Scalars ..
  148:       INTEGER            I, J, JC
  149:       DOUBLE PRECISION   CJ, LARGE, SMALL
  150: *     ..
  151: *     .. External Functions ..
  152:       LOGICAL            LSAME
  153:       DOUBLE PRECISION   DLAMCH
  154:       EXTERNAL           LSAME, DLAMCH
  155: *     ..
  156: *     .. Executable Statements ..
  157: *
  158: *     Quick return if possible
  159: *
  160:       IF( N.LE.0 ) THEN
  161:          EQUED = 'N'
  162:          RETURN
  163:       END IF
  164: *
  165: *     Initialize LARGE and SMALL.
  166: *
  167:       SMALL = DLAMCH( 'Safe minimum' ) / DLAMCH( 'Precision' )
  168:       LARGE = ONE / SMALL
  169: *
  170:       IF( SCOND.GE.THRESH .AND. AMAX.GE.SMALL .AND. AMAX.LE.LARGE ) THEN
  171: *
  172: *        No equilibration
  173: *
  174:          EQUED = 'N'
  175:       ELSE
  176: *
  177: *        Replace A by diag(S) * A * diag(S).
  178: *
  179:          IF( LSAME( UPLO, 'U' ) ) THEN
  180: *
  181: *           Upper triangle of A is stored.
  182: *
  183:             JC = 1
  184:             DO 20 J = 1, N
  185:                CJ = S( J )
  186:                DO 10 I = 1, J
  187:                   AP( JC+I-1 ) = CJ*S( I )*AP( JC+I-1 )
  188:    10          CONTINUE
  189:                JC = JC + J
  190:    20       CONTINUE
  191:          ELSE
  192: *
  193: *           Lower triangle of A is stored.
  194: *
  195:             JC = 1
  196:             DO 40 J = 1, N
  197:                CJ = S( J )
  198:                DO 30 I = J, N
  199:                   AP( JC+I-J ) = CJ*S( I )*AP( JC+I-J )
  200:    30          CONTINUE
  201:                JC = JC + N - J + 1
  202:    40       CONTINUE
  203:          END IF
  204:          EQUED = 'Y'
  205:       END IF
  206: *
  207:       RETURN
  208: *
  209: *     End of ZLAQSP
  210: *
  211:       END