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1 SUBROUTINE DRSCL( N, SA, SX, INCX ) |
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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 SA |
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10 * .. |
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11 * .. Array Arguments .. |
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12 DOUBLE PRECISION SX( * ) |
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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 * DRSCL multiplies an n-element real vector x by the real scalar 1/a. |
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19 * This is done without overflow or underflow as long as |
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20 * the final result x/a does not overflow or underflow. |
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21 * |
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22 * Arguments |
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23 * ========= |
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24 * |
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25 * N (input) INTEGER |
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26 * The number of components of the vector x. |
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27 * |
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28 * SA (input) DOUBLE PRECISION |
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29 * The scalar a which is used to divide each component of x. |
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30 * SA must be >= 0, or the subroutine will divide by zero. |
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31 * |
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32 * SX (input/output) DOUBLE PRECISION array, dimension |
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33 * (1+(N-1)*abs(INCX)) |
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34 * The n-element vector x. |
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35 * |
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36 * INCX (input) INTEGER |
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37 * The increment between successive values of the vector SX. |
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38 * > 0: SX(1) = X(1) and SX(1+(i-1)*INCX) = x(i), 1< i<= n |
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39 * |
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40 * ===================================================================== |
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41 * |
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42 * .. Parameters .. |
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43 DOUBLE PRECISION ONE, ZERO |
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44 PARAMETER ( ONE = 1.0D+0, ZERO = 0.0D+0 ) |
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45 * .. |
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46 * .. Local Scalars .. |
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47 LOGICAL DONE |
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48 DOUBLE PRECISION BIGNUM, CDEN, CDEN1, CNUM, CNUM1, MUL, SMLNUM |
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49 * .. |
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50 * .. External Functions .. |
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51 DOUBLE PRECISION DLAMCH |
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52 EXTERNAL DLAMCH |
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53 * .. |
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54 * .. External Subroutines .. |
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55 EXTERNAL DSCAL |
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56 * .. |
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57 * .. Intrinsic Functions .. |
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58 INTRINSIC ABS |
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59 * .. |
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60 * .. Executable Statements .. |
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61 * |
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62 * Quick return if possible |
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63 * |
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64 IF( N.LE.0 ) |
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65 $ RETURN |
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66 * |
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67 * Get machine parameters |
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68 * |
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69 SMLNUM = DLAMCH( 'S' ) |
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70 BIGNUM = ONE / SMLNUM |
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71 CALL DLABAD( SMLNUM, BIGNUM ) |
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72 * |
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73 * Initialize the denominator to SA and the numerator to 1. |
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74 * |
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75 CDEN = SA |
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76 CNUM = ONE |
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77 * |
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78 10 CONTINUE |
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79 CDEN1 = CDEN*SMLNUM |
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80 CNUM1 = CNUM / BIGNUM |
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81 IF( ABS( CDEN1 ).GT.ABS( CNUM ) .AND. CNUM.NE.ZERO ) THEN |
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82 * |
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83 * Pre-multiply X by SMLNUM if CDEN is large compared to CNUM. |
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84 * |
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85 MUL = SMLNUM |
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86 DONE = .FALSE. |
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87 CDEN = CDEN1 |
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88 ELSE IF( ABS( CNUM1 ).GT.ABS( CDEN ) ) THEN |
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89 * |
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90 * Pre-multiply X by BIGNUM if CDEN is small compared to CNUM. |
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91 * |
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92 MUL = BIGNUM |
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93 DONE = .FALSE. |
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94 CNUM = CNUM1 |
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95 ELSE |
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96 * |
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97 * Multiply X by CNUM / CDEN and return. |
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98 * |
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99 MUL = CNUM / CDEN |
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100 DONE = .TRUE. |
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101 END IF |
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102 * |
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103 * Scale the vector X by MUL |
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104 * |
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105 CALL DSCAL( N, MUL, SX, INCX ) |
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106 * |
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107 IF( .NOT.DONE ) |
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108 $ GO TO 10 |
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109 * |
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110 RETURN |
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111 * |
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112 * End of DRSCL |
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113 * |
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114 END |
