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Annotation of rpl/lapack/lapack/zlassq.f, revision 1.6

1.1       bertrand    1:       SUBROUTINE ZLASSQ( N, X, INCX, SCALE, SUMSQ )
                      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:       INTEGER            INCX, N
                     10:       DOUBLE PRECISION   SCALE, SUMSQ
                     11: *     ..
                     12: *     .. Array Arguments ..
                     13:       COMPLEX*16         X( * )
                     14: *     ..
                     15: *
                     16: *  Purpose
                     17: *  =======
                     18: *
                     19: *  ZLASSQ returns the values scl and ssq such that
                     20: *
                     21: *     ( scl**2 )*ssq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,
                     22: *
                     23: *  where x( i ) = abs( X( 1 + ( i - 1 )*INCX ) ). The value of sumsq is
                     24: *  assumed to be at least unity and the value of ssq will then satisfy
                     25: *
                     26: *     1.0 .le. ssq .le. ( sumsq + 2*n ).
                     27: *
                     28: *  scale is assumed to be non-negative and scl returns the value
                     29: *
                     30: *     scl = max( scale, abs( real( x( i ) ) ), abs( aimag( x( i ) ) ) ),
                     31: *            i
                     32: *
                     33: *  scale and sumsq must be supplied in SCALE and SUMSQ respectively.
                     34: *  SCALE and SUMSQ are overwritten by scl and ssq respectively.
                     35: *
                     36: *  The routine makes only one pass through the vector X.
                     37: *
                     38: *  Arguments
                     39: *  =========
                     40: *
                     41: *  N       (input) INTEGER
                     42: *          The number of elements to be used from the vector X.
                     43: *
                     44: *  X       (input) COMPLEX*16 array, dimension (N)
                     45: *          The vector x as described above.
                     46: *             x( i )  = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.
                     47: *
                     48: *  INCX    (input) INTEGER
                     49: *          The increment between successive values of the vector X.
                     50: *          INCX > 0.
                     51: *
                     52: *  SCALE   (input/output) DOUBLE PRECISION
                     53: *          On entry, the value  scale  in the equation above.
                     54: *          On exit, SCALE is overwritten with the value  scl .
                     55: *
                     56: *  SUMSQ   (input/output) DOUBLE PRECISION
                     57: *          On entry, the value  sumsq  in the equation above.
                     58: *          On exit, SUMSQ is overwritten with the value  ssq .
                     59: *
                     60: * =====================================================================
                     61: *
                     62: *     .. Parameters ..
                     63:       DOUBLE PRECISION   ZERO
                     64:       PARAMETER          ( ZERO = 0.0D+0 )
                     65: *     ..
                     66: *     .. Local Scalars ..
                     67:       INTEGER            IX
                     68:       DOUBLE PRECISION   TEMP1
                     69: *     ..
                     70: *     .. Intrinsic Functions ..
                     71:       INTRINSIC          ABS, DBLE, DIMAG
                     72: *     ..
                     73: *     .. Executable Statements ..
                     74: *
                     75:       IF( N.GT.0 ) THEN
                     76:          DO 10 IX = 1, 1 + ( N-1 )*INCX, INCX
                     77:             IF( DBLE( X( IX ) ).NE.ZERO ) THEN
                     78:                TEMP1 = ABS( DBLE( X( IX ) ) )
                     79:                IF( SCALE.LT.TEMP1 ) THEN
                     80:                   SUMSQ = 1 + SUMSQ*( SCALE / TEMP1 )**2
                     81:                   SCALE = TEMP1
                     82:                ELSE
                     83:                   SUMSQ = SUMSQ + ( TEMP1 / SCALE )**2
                     84:                END IF
                     85:             END IF
                     86:             IF( DIMAG( X( IX ) ).NE.ZERO ) THEN
                     87:                TEMP1 = ABS( DIMAG( X( IX ) ) )
                     88:                IF( SCALE.LT.TEMP1 ) THEN
                     89:                   SUMSQ = 1 + SUMSQ*( SCALE / TEMP1 )**2
                     90:                   SCALE = TEMP1
                     91:                ELSE
                     92:                   SUMSQ = SUMSQ + ( TEMP1 / SCALE )**2
                     93:                END IF
                     94:             END IF
                     95:    10    CONTINUE
                     96:       END IF
                     97: *
                     98:       RETURN
                     99: *
                    100: *     End of ZLASSQ
                    101: *
                    102:       END