classq.f

          SUBROUTINE CLASSQ( N, X, INCX, SCALE, SUMSQ )
    *
    *  -- LAPACK auxiliary routine (version 3.1) --
    *     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
    *     November 2006
    *
    *     .. Scalar Arguments ..
          INTEGER            INCX, N
          REAL               SCALE, SUMSQ
    *     ..
    *     .. Array Arguments ..
          COMPLEX            X( * )
    *     ..
    *
    *  Purpose
    *  =======
    *
    *  CLASSQ returns the values scl and ssq such that
    *
    *     ( scl**2 )*ssq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,
    *
    *  where x( i ) = abs( X( 1 + ( i - 1 )*INCX ) ). The value of sumsq is
    *  assumed to be at least unity and the value of ssq will then satisfy
    *
    *     1.0 .le. ssq .le. ( sumsq + 2*n ).
    *
    *  scale is assumed to be non-negative and scl returns the value
    *
    *     scl = max( scale, abs( real( x( i ) ) ), abs( aimag( x( i ) ) ) ),
    *            i
    *
    *  scale and sumsq must be supplied in SCALE and SUMSQ respectively.
    *  SCALE and SUMSQ are overwritten by scl and ssq respectively.
    *
    *  The routine makes only one pass through the vector X.
    *
    *  Arguments
    *  =========
    *
    *  N       (input) INTEGER
    *          The number of elements to be used from the vector X.
    *
    *  X       (input) COMPLEX array, dimension (N)
    *          The vector x as described above.
    *             x( i )  = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.
    *
    *  INCX    (input) INTEGER
    *          The increment between successive values of the vector X.
    *          INCX > 0.
    *
    *  SCALE   (input/output) REAL
    *          On entry, the value  scale  in the equation above.
    *          On exit, SCALE is overwritten with the value  scl .
    *
    *  SUMSQ   (input/output) REAL
    *          On entry, the value  sumsq  in the equation above.
    *          On exit, SUMSQ is overwritten with the value  ssq .
    *
    * =====================================================================
    *
    *     .. Parameters ..
          REAL               ZERO
          PARAMETER          ( ZERO = 0.0E+0 )
    *     ..
    *     .. Local Scalars ..
          INTEGER            IX
          REAL               TEMP1
    *     ..
    *     .. Intrinsic Functions ..
          INTRINSIC          ABS, AIMAG, REAL
    *     ..
    *     .. Executable Statements ..
    *
          IF( N.GT.0 ) THEN
             DO 10 IX = 1, 1 + ( N-1 )*INCX, INCX
                IF( REAL( X( IX ) ).NE.ZERO ) THEN
                   TEMP1 = ABS( REAL( X( IX ) ) )
                   IF( SCALE.LT.TEMP1 ) THEN
                      SUMSQ = 1 + SUMSQ*( SCALE / TEMP1 )**2
                      SCALE = TEMP1
                   ELSE
                      SUMSQ = SUMSQ + ( TEMP1 / SCALE )**2
                   END IF
                END IF
                IF( AIMAG( X( IX ) ).NE.ZERO ) THEN
                   TEMP1 = ABS( AIMAG( X( IX ) ) )
                   IF( SCALE.LT.TEMP1 ) THEN
                      SUMSQ = 1 + SUMSQ*( SCALE / TEMP1 )**2
                      SCALE = TEMP1
                   ELSE
                      SUMSQ = SUMSQ + ( TEMP1 / SCALE )**2
                   END IF
                END IF
       10    CONTINUE
          END IF
    *
          RETURN
    *
    *     End of CLASSQ
    *
          END