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[project @ 2004-11-19 21:50:50 by jwe]
author jwe
date Fri, 19 Nov 2004 21:50:50 +0000
parents 15cddaacbc2d
children 68db500cb558
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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 3.0) --
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4 * Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,
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5 * Courant Institute, Argonne National Lab, and Rice University
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6 * June 30, 1999
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7 *
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8 * .. Scalar Arguments ..
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9 INTEGER INCX, N
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10 DOUBLE PRECISION SCALE, SUMSQ
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11 * ..
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12 * .. Array Arguments ..
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13 DOUBLE PRECISION X( * )
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14 * ..
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15 *
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16 * Purpose
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17 * =======
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18 *
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19 * DLASSQ returns the values scl and smsq such that
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20 *
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21 * ( scl**2 )*smsq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,
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22 *
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23 * where x( i ) = X( 1 + ( i - 1 )*INCX ). The value of sumsq is
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24 * assumed to be non-negative and scl returns the value
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25 *
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26 * scl = max( scale, abs( x( i ) ) ).
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27 *
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28 * scale and sumsq must be supplied in SCALE and SUMSQ and
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29 * scl and smsq are overwritten on SCALE and SUMSQ respectively.
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30 *
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31 * The routine makes only one pass through the vector x.
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32 *
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33 * Arguments
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34 * =========
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35 *
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36 * N (input) INTEGER
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37 * The number of elements to be used from the vector X.
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38 *
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39 * X (input) DOUBLE PRECISION array, dimension (N)
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40 * The vector for which a scaled sum of squares is computed.
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41 * x( i ) = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.
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42 *
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43 * INCX (input) INTEGER
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44 * The increment between successive values of the vector X.
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45 * INCX > 0.
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46 *
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47 * SCALE (input/output) DOUBLE PRECISION
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48 * On entry, the value scale in the equation above.
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49 * On exit, SCALE is overwritten with scl , the scaling factor
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50 * for the sum of squares.
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51 *
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52 * SUMSQ (input/output) DOUBLE PRECISION
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53 * On entry, the value sumsq in the equation above.
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54 * On exit, SUMSQ is overwritten with smsq , the basic sum of
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55 * squares from which scl has been factored out.
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56 *
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57 * =====================================================================
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58 *
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59 * .. Parameters ..
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60 DOUBLE PRECISION ZERO
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61 PARAMETER ( ZERO = 0.0D+0 )
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62 * ..
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63 * .. Local Scalars ..
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64 INTEGER IX
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65 DOUBLE PRECISION ABSXI
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66 * ..
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67 * .. Intrinsic Functions ..
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68 INTRINSIC ABS
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69 * ..
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70 * .. Executable Statements ..
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71 *
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72 IF( N.GT.0 ) THEN
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73 DO 10 IX = 1, 1 + ( N-1 )*INCX, INCX
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74 IF( X( IX ).NE.ZERO ) THEN
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75 ABSXI = ABS( X( IX ) )
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76 IF( SCALE.LT.ABSXI ) THEN
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77 SUMSQ = 1 + SUMSQ*( SCALE / ABSXI )**2
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78 SCALE = ABSXI
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79 ELSE
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80 SUMSQ = SUMSQ + ( ABSXI / SCALE )**2
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81 END IF
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82 END IF
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83 10 CONTINUE
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84 END IF
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85 RETURN
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86 *
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87 * End of DLASSQ
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88 *
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89 END