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    1: *> \brief \b DLAPY2 returns sqrt(x2+y2).
    2: *
    3: *  =========== DOCUMENTATION ===========
    4: *
    5: * Online html documentation available at
    6: *            http://www.netlib.org/lapack/explore-html/
    7: *
    8: *> \htmlonly
    9: *> Download DLAPY2 + dependencies
   10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/dlapy2.f">
   11: *> [TGZ]</a>
   12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/dlapy2.f">
   13: *> [ZIP]</a>
   14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/dlapy2.f">
   15: *> [TXT]</a>
   16: *> \endhtmlonly
   17: *
   18: *  Definition:
   19: *  ===========
   20: *
   21: *       DOUBLE PRECISION FUNCTION DLAPY2( X, Y )
   22: *
   23: *       .. Scalar Arguments ..
   24: *       DOUBLE PRECISION   X, Y
   25: *       ..
   26: *
   27: *
   28: *> \par Purpose:
   29: *  =============
   30: *>
   31: *> \verbatim
   32: *>
   33: *> DLAPY2 returns sqrt(x**2+y**2), taking care not to cause unnecessary
   34: *> overflow and unnecessary underflow.
   35: *> \endverbatim
   36: *
   37: *  Arguments:
   38: *  ==========
   39: *
   40: *> \param[in] X
   41: *> \verbatim
   42: *>          X is DOUBLE PRECISION
   43: *> \endverbatim
   44: *>
   45: *> \param[in] Y
   46: *> \verbatim
   47: *>          Y is DOUBLE PRECISION
   48: *>          X and Y specify the values x and y.
   49: *> \endverbatim
   50: *
   51: *  Authors:
   52: *  ========
   53: *
   54: *> \author Univ. of Tennessee
   55: *> \author Univ. of California Berkeley
   56: *> \author Univ. of Colorado Denver
   57: *> \author NAG Ltd.
   58: *
   59: *> \ingroup OTHERauxiliary
   60: *
   61: *  =====================================================================
   62:       DOUBLE PRECISION FUNCTION DLAPY2( X, Y )
   63: *
   64: *  -- LAPACK auxiliary routine --
   65: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
   66: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
   67: *
   68: *     .. Scalar Arguments ..
   69:       DOUBLE PRECISION   X, Y
   70: *     ..
   71: *
   72: *  =====================================================================
   73: *
   74: *     .. Parameters ..
   75:       DOUBLE PRECISION   ZERO
   76:       PARAMETER          ( ZERO = 0.0D0 )
   77:       DOUBLE PRECISION   ONE
   78:       PARAMETER          ( ONE = 1.0D0 )
   79: *     ..
   80: *     .. Local Scalars ..
   81:       DOUBLE PRECISION   W, XABS, YABS, Z, HUGEVAL
   82:       LOGICAL            X_IS_NAN, Y_IS_NAN
   83: *     ..
   84: *     .. External Functions ..
   85:       LOGICAL            DISNAN
   86:       EXTERNAL           DISNAN
   87: *     ..
   88: *     .. External Subroutines ..
   89:       DOUBLE PRECISION   DLAMCH
   90: *     ..
   91: *     .. Intrinsic Functions ..
   92:       INTRINSIC          ABS, MAX, MIN, SQRT
   93: *     ..
   94: *     .. Executable Statements ..
   95: *
   96:       X_IS_NAN = DISNAN( X )
   97:       Y_IS_NAN = DISNAN( Y )
   98:       IF ( X_IS_NAN ) DLAPY2 = X
   99:       IF ( Y_IS_NAN ) DLAPY2 = Y
  100:       HUGEVAL = DLAMCH( 'Overflow' )
  101: *
  102:       IF ( .NOT.( X_IS_NAN.OR.Y_IS_NAN ) ) THEN
  103:          XABS = ABS( X )
  104:          YABS = ABS( Y )
  105:          W = MAX( XABS, YABS )
  106:          Z = MIN( XABS, YABS )
  107:          IF( Z.EQ.ZERO .OR. W.GT.HUGEVAL ) THEN
  108:             DLAPY2 = W
  109:          ELSE
  110:             DLAPY2 = W*SQRT( ONE+( Z / W )**2 )
  111:          END IF
  112:       END IF
  113:       RETURN
  114: *
  115: *     End of DLAPY2
  116: *
  117:       END