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Annotation of rpl/lapack/lapack/dlapy3.f, revision 1.2

1.1       bertrand    1:       DOUBLE PRECISION FUNCTION DLAPY3( X, Y, Z )
                      2: *
                      3: *  -- LAPACK auxiliary routine (version 3.2) --
                      4: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
                      5: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
                      6: *     November 2006
                      7: *
                      8: *     .. Scalar Arguments ..
                      9:       DOUBLE PRECISION   X, Y, Z
                     10: *     ..
                     11: *
                     12: *  Purpose
                     13: *  =======
                     14: *
                     15: *  DLAPY3 returns sqrt(x**2+y**2+z**2), taking care not to cause
                     16: *  unnecessary overflow.
                     17: *
                     18: *  Arguments
                     19: *  =========
                     20: *
                     21: *  X       (input) DOUBLE PRECISION
                     22: *  Y       (input) DOUBLE PRECISION
                     23: *  Z       (input) DOUBLE PRECISION
                     24: *          X, Y and Z specify the values x, y and z.
                     25: *
                     26: *  =====================================================================
                     27: *
                     28: *     .. Parameters ..
                     29:       DOUBLE PRECISION   ZERO
                     30:       PARAMETER          ( ZERO = 0.0D0 )
                     31: *     ..
                     32: *     .. Local Scalars ..
                     33:       DOUBLE PRECISION   W, XABS, YABS, ZABS
                     34: *     ..
                     35: *     .. Intrinsic Functions ..
                     36:       INTRINSIC          ABS, MAX, SQRT
                     37: *     ..
                     38: *     .. Executable Statements ..
                     39: *
                     40:       XABS = ABS( X )
                     41:       YABS = ABS( Y )
                     42:       ZABS = ABS( Z )
                     43:       W = MAX( XABS, YABS, ZABS )
                     44:       IF( W.EQ.ZERO ) THEN
                     45: *     W can be zero for max(0,nan,0)
                     46: *     adding all three entries together will make sure
                     47: *     NaN will not disappear.
                     48:          DLAPY3 =  XABS + YABS + ZABS
                     49:       ELSE
                     50:          DLAPY3 = W*SQRT( ( XABS / W )**2+( YABS / W )**2+
                     51:      $            ( ZABS / W )**2 )
                     52:       END IF
                     53:       RETURN
                     54: *
                     55: *     End of DLAPY3
                     56: *
                     57:       END