SUBROUTINE ZLASSQ( N, X, INCX, SCALE, SUMSQ ) * * -- LAPACK auxiliary routine (version 3.2) -- * -- LAPACK is a software package provided by Univ. of Tennessee, -- * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- * November 2006 * * .. Scalar Arguments .. INTEGER INCX, N DOUBLE PRECISION SCALE, SUMSQ * .. * .. Array Arguments .. COMPLEX*16 X( * ) * .. * * Purpose * ======= * * ZLASSQ 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*16 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) DOUBLE PRECISION * On entry, the value scale in the equation above. * On exit, SCALE is overwritten with the value scl . * * SUMSQ (input/output) DOUBLE PRECISION * On entry, the value sumsq in the equation above. * On exit, SUMSQ is overwritten with the value ssq . * * ===================================================================== * * .. Parameters .. DOUBLE PRECISION ZERO PARAMETER ( ZERO = 0.0D+0 ) * .. * .. Local Scalars .. INTEGER IX DOUBLE PRECISION TEMP1 * .. * .. Intrinsic Functions .. INTRINSIC ABS, DBLE, DIMAG * .. * .. Executable Statements .. * IF( N.GT.0 ) THEN DO 10 IX = 1, 1 + ( N-1 )*INCX, INCX IF( DBLE( X( IX ) ).NE.ZERO ) THEN TEMP1 = ABS( DBLE( 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( DIMAG( X( IX ) ).NE.ZERO ) THEN TEMP1 = ABS( DIMAG( 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 ZLASSQ * END