Annotation of rpl/lapack/lapack/zlassq.f, revision 1.1
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
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