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[project @ 2007-10-16 18:54:19 by jwe]
author jwe
date Tue, 16 Oct 2007 18:54:23 +0000
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children
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1 SUBROUTINE DLASSQ( N, X, INCX, SCALE, SUMSQ )
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2 *
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3 * -- LAPACK auxiliary routine (version 3.1) --
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4 * Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
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5 * November 2006
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6 *
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7 * .. Scalar Arguments ..
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8 INTEGER INCX, N
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9 DOUBLE PRECISION SCALE, SUMSQ
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10 * ..
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11 * .. Array Arguments ..
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12 DOUBLE PRECISION X( * )
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13 * ..
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14 *
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15 * Purpose
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16 * =======
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17 *
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18 * DLASSQ returns the values scl and smsq such that
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19 *
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20 * ( scl**2 )*smsq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,
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21 *
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22 * where x( i ) = X( 1 + ( i - 1 )*INCX ). The value of sumsq is
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23 * assumed to be non-negative and scl returns the value
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24 *
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25 * scl = max( scale, abs( x( i ) ) ).
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26 *
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27 * scale and sumsq must be supplied in SCALE and SUMSQ and
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28 * scl and smsq are overwritten on SCALE and SUMSQ respectively.
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29 *
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30 * The routine makes only one pass through the vector x.
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31 *
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32 * Arguments
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33 * =========
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34 *
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35 * N (input) INTEGER
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36 * The number of elements to be used from the vector X.
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37 *
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38 * X (input) DOUBLE PRECISION array, dimension (N)
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39 * The vector for which a scaled sum of squares is computed.
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40 * x( i ) = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.
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41 *
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42 * INCX (input) INTEGER
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43 * The increment between successive values of the vector X.
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44 * INCX > 0.
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45 *
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46 * SCALE (input/output) DOUBLE PRECISION
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47 * On entry, the value scale in the equation above.
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48 * On exit, SCALE is overwritten with scl , the scaling factor
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49 * for the sum of squares.
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50 *
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51 * SUMSQ (input/output) DOUBLE PRECISION
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52 * On entry, the value sumsq in the equation above.
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53 * On exit, SUMSQ is overwritten with smsq , the basic sum of
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54 * squares from which scl has been factored out.
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55 *
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56 * =====================================================================
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57 *
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58 * .. Parameters ..
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59 DOUBLE PRECISION ZERO
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60 PARAMETER ( ZERO = 0.0D+0 )
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61 * ..
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62 * .. Local Scalars ..
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63 INTEGER IX
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64 DOUBLE PRECISION ABSXI
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65 * ..
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66 * .. Intrinsic Functions ..
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67 INTRINSIC ABS
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68 * ..
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69 * .. Executable Statements ..
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70 *
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71 IF( N.GT.0 ) THEN
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72 DO 10 IX = 1, 1 + ( N-1 )*INCX, INCX
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73 IF( X( IX ).NE.ZERO ) THEN
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74 ABSXI = ABS( X( IX ) )
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75 IF( SCALE.LT.ABSXI ) THEN
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76 SUMSQ = 1 + SUMSQ*( SCALE / ABSXI )**2
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77 SCALE = ABSXI
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78 ELSE
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79 SUMSQ = SUMSQ + ( ABSXI / SCALE )**2
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80 END IF
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81 END IF
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82 10 CONTINUE
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83 END IF
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84 RETURN
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85 *
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86 * End of DLASSQ
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87 *
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88 END