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    1: *> \brief \b DLAQSY
    2: *
    3: *  =========== DOCUMENTATION ===========
    4: *
    5: * Online html documentation available at 
    6: *            http://www.netlib.org/lapack/explore-html/ 
    7: *
    8: *> \htmlonly
    9: *> Download DLAQSY + dependencies 
   10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlaqsy.f"> 
   11: *> [TGZ]</a> 
   12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlaqsy.f"> 
   13: *> [ZIP]</a> 
   14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlaqsy.f"> 
   15: *> [TXT]</a>
   16: *> \endhtmlonly 
   17: *
   18: *  Definition:
   19: *  ===========
   20: *
   21: *       SUBROUTINE DLAQSY( UPLO, N, A, LDA, S, SCOND, AMAX, EQUED )
   22: * 
   23: *       .. Scalar Arguments ..
   24: *       CHARACTER          EQUED, UPLO
   25: *       INTEGER            LDA, N
   26: *       DOUBLE PRECISION   AMAX, SCOND
   27: *       ..
   28: *       .. Array Arguments ..
   29: *       DOUBLE PRECISION   A( LDA, * ), S( * )
   30: *       ..
   31: *  
   32: *
   33: *> \par Purpose:
   34: *  =============
   35: *>
   36: *> \verbatim
   37: *>
   38: *> DLAQSY equilibrates a symmetric matrix A using the scaling factors
   39: *> in the vector S.
   40: *> \endverbatim
   41: *
   42: *  Arguments:
   43: *  ==========
   44: *
   45: *> \param[in] UPLO
   46: *> \verbatim
   47: *>          UPLO is CHARACTER*1
   48: *>          Specifies whether the upper or lower triangular part of the
   49: *>          symmetric matrix A is stored.
   50: *>          = 'U':  Upper triangular
   51: *>          = 'L':  Lower triangular
   52: *> \endverbatim
   53: *>
   54: *> \param[in] N
   55: *> \verbatim
   56: *>          N is INTEGER
   57: *>          The order of the matrix A.  N >= 0.
   58: *> \endverbatim
   59: *>
   60: *> \param[in,out] A
   61: *> \verbatim
   62: *>          A is DOUBLE PRECISION array, dimension (LDA,N)
   63: *>          On entry, the symmetric matrix A.  If UPLO = 'U', the leading
   64: *>          n by n upper triangular part of A contains the upper
   65: *>          triangular part of the matrix A, and the strictly lower
   66: *>          triangular part of A is not referenced.  If UPLO = 'L', the
   67: *>          leading n by n lower triangular part of A contains the lower
   68: *>          triangular part of the matrix A, and the strictly upper
   69: *>          triangular part of A is not referenced.
   70: *>
   71: *>          On exit, if EQUED = 'Y', the equilibrated matrix:
   72: *>          diag(S) * A * diag(S).
   73: *> \endverbatim
   74: *>
   75: *> \param[in] LDA
   76: *> \verbatim
   77: *>          LDA is INTEGER
   78: *>          The leading dimension of the array A.  LDA >= max(N,1).
   79: *> \endverbatim
   80: *>
   81: *> \param[in] S
   82: *> \verbatim
   83: *>          S is DOUBLE PRECISION array, dimension (N)
   84: *>          The scale factors for A.
   85: *> \endverbatim
   86: *>
   87: *> \param[in] SCOND
   88: *> \verbatim
   89: *>          SCOND is DOUBLE PRECISION
   90: *>          Ratio of the smallest S(i) to the largest S(i).
   91: *> \endverbatim
   92: *>
   93: *> \param[in] AMAX
   94: *> \verbatim
   95: *>          AMAX is DOUBLE PRECISION
   96: *>          Absolute value of largest matrix entry.
   97: *> \endverbatim
   98: *>
   99: *> \param[out] EQUED
  100: *> \verbatim
  101: *>          EQUED is CHARACTER*1
  102: *>          Specifies whether or not equilibration was done.
  103: *>          = 'N':  No equilibration.
  104: *>          = 'Y':  Equilibration was done, i.e., A has been replaced by
  105: *>                  diag(S) * A * diag(S).
  106: *> \endverbatim
  107: *
  108: *> \par Internal Parameters:
  109: *  =========================
  110: *>
  111: *> \verbatim
  112: *>  THRESH is a threshold value used to decide if scaling should be done
  113: *>  based on the ratio of the scaling factors.  If SCOND < THRESH,
  114: *>  scaling is done.
  115: *>
  116: *>  LARGE and SMALL are threshold values used to decide if scaling should
  117: *>  be done based on the absolute size of the largest matrix element.
  118: *>  If AMAX > LARGE or AMAX < SMALL, scaling is done.
  119: *> \endverbatim
  120: *
  121: *  Authors:
  122: *  ========
  123: *
  124: *> \author Univ. of Tennessee 
  125: *> \author Univ. of California Berkeley 
  126: *> \author Univ. of Colorado Denver 
  127: *> \author NAG Ltd. 
  128: *
  129: *> \date November 2011
  130: *
  131: *> \ingroup doubleSYauxiliary
  132: *
  133: *  =====================================================================
  134:       SUBROUTINE DLAQSY( UPLO, N, A, LDA, S, SCOND, AMAX, EQUED )
  135: *
  136: *  -- LAPACK auxiliary routine (version 3.4.0) --
  137: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
  138: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
  139: *     November 2011
  140: *
  141: *     .. Scalar Arguments ..
  142:       CHARACTER          EQUED, UPLO
  143:       INTEGER            LDA, N
  144:       DOUBLE PRECISION   AMAX, SCOND
  145: *     ..
  146: *     .. Array Arguments ..
  147:       DOUBLE PRECISION   A( LDA, * ), S( * )
  148: *     ..
  149: *
  150: *  =====================================================================
  151: *
  152: *     .. Parameters ..
  153:       DOUBLE PRECISION   ONE, THRESH
  154:       PARAMETER          ( ONE = 1.0D+0, THRESH = 0.1D+0 )
  155: *     ..
  156: *     .. Local Scalars ..
  157:       INTEGER            I, J
  158:       DOUBLE PRECISION   CJ, LARGE, SMALL
  159: *     ..
  160: *     .. External Functions ..
  161:       LOGICAL            LSAME
  162:       DOUBLE PRECISION   DLAMCH
  163:       EXTERNAL           LSAME, DLAMCH
  164: *     ..
  165: *     .. Executable Statements ..
  166: *
  167: *     Quick return if possible
  168: *
  169:       IF( N.LE.0 ) THEN
  170:          EQUED = 'N'
  171:          RETURN
  172:       END IF
  173: *
  174: *     Initialize LARGE and SMALL.
  175: *
  176:       SMALL = DLAMCH( 'Safe minimum' ) / DLAMCH( 'Precision' )
  177:       LARGE = ONE / SMALL
  178: *
  179:       IF( SCOND.GE.THRESH .AND. AMAX.GE.SMALL .AND. AMAX.LE.LARGE ) THEN
  180: *
  181: *        No equilibration
  182: *
  183:          EQUED = 'N'
  184:       ELSE
  185: *
  186: *        Replace A by diag(S) * A * diag(S).
  187: *
  188:          IF( LSAME( UPLO, 'U' ) ) THEN
  189: *
  190: *           Upper triangle of A is stored.
  191: *
  192:             DO 20 J = 1, N
  193:                CJ = S( J )
  194:                DO 10 I = 1, J
  195:                   A( I, J ) = CJ*S( I )*A( I, J )
  196:    10          CONTINUE
  197:    20       CONTINUE
  198:          ELSE
  199: *
  200: *           Lower triangle of A is stored.
  201: *
  202:             DO 40 J = 1, N
  203:                CJ = S( J )
  204:                DO 30 I = J, N
  205:                   A( I, J ) = CJ*S( I )*A( I, J )
  206:    30          CONTINUE
  207:    40       CONTINUE
  208:          END IF
  209:          EQUED = 'Y'
  210:       END IF
  211: *
  212:       RETURN
  213: *
  214: *     End of DLAQSY
  215: *
  216:       END