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1 /* ========================================================================== */ |
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2 /* === UMF_scale ============================================================ */ |
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3 /* ========================================================================== */ |
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4 |
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5 /* -------------------------------------------------------------------------- */ |
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6 /* UMFPACK Version 4.4, Copyright (c) 2005 by Timothy A. Davis. CISE Dept, */ |
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7 /* Univ. of Florida. All Rights Reserved. See ../Doc/License for License. */ |
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8 /* web: http://www.cise.ufl.edu/research/sparse/umfpack */ |
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9 /* -------------------------------------------------------------------------- */ |
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10 |
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11 /* Divide a vector of stride 1 by the pivot value. */ |
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12 |
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13 #include "umf_internal.h" |
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14 |
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15 GLOBAL void UMF_scale |
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16 ( |
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17 Int n, |
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18 Entry pivot, |
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19 Entry X [ ] |
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20 ) |
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21 { |
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22 Entry x ; |
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23 double s ; |
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24 Int i ; |
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25 |
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26 /* ---------------------------------------------------------------------- */ |
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27 /* compute the approximate absolute value of the pivot, and select method */ |
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28 /* ---------------------------------------------------------------------- */ |
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29 |
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30 APPROX_ABS (s, pivot) ; |
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31 |
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32 if (s < RECIPROCAL_TOLERANCE || IS_NAN (pivot)) |
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33 { |
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34 /* ------------------------------------------------------------------ */ |
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35 /* tiny, or zero, pivot case */ |
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36 /* ------------------------------------------------------------------ */ |
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37 |
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38 /* The pivot is tiny, or NaN. Do not divide zero by the pivot value, |
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39 * and do not multiply by 1/pivot, either. */ |
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40 |
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41 for (i = 0 ; i < n ; i++) |
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42 { |
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43 /* X [i] /= pivot ; */ |
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44 x = X [i] ; |
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45 |
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46 #ifndef NO_DIVIDE_BY_ZERO |
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47 if (IS_NONZERO (x)) |
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48 { |
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49 DIV (X [i], x, pivot) ; |
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50 } |
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51 #else |
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52 /* Do not divide by zero */ |
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53 if (IS_NONZERO (x) && IS_NONZERO (pivot)) |
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54 { |
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55 DIV (X [i], x, pivot) ; |
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56 } |
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57 #endif |
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58 |
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59 } |
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60 |
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61 } |
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62 else |
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63 { |
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64 |
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65 /* ------------------------------------------------------------------ */ |
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66 /* normal case. select the x/pivot or x * (1/pivot) method */ |
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67 /* ------------------------------------------------------------------ */ |
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68 |
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69 /* The pivot is not tiny, and is not NaN. Don't bother to check for |
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70 * zeros in the pivot column, X. */ |
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71 |
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72 #if !defined (NRECIPROCAL) && !(defined (__GNUC__) && defined (COMPLEX)) |
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73 |
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74 /* -------------------------------------------------------------- */ |
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75 /* multiply x by (1/pivot) */ |
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76 /* -------------------------------------------------------------- */ |
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77 |
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78 /* Slightly less accurate, but faster. It allows the use of |
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79 * the level-1 BLAS dscal or zscal routine. This not used when |
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80 * UMFPACK is used in MATLAB (either as a built-in routine, or as |
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81 * a mexFunction). |
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82 * |
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83 * Using gcc version 3.2 can cause the following code to fail for |
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84 * some complex matrices (not all), with or without the BLAS. This |
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85 * was found in Red Hat Linux 7.3 on a Dell Latitude C840 with a |
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86 * Pentium 4M. Thus, this code is not used when gcc is used, for |
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87 * the complex case. |
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88 * |
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89 * It works just fine with Intel's icc compiler, version 7.0. |
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90 */ |
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91 |
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92 /* pivot = 1 / pivot */ |
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93 RECIPROCAL (pivot) ; |
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94 |
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95 #if defined (USE_NO_BLAS) |
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96 for (i = 0 ; i < n ; i++) |
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97 { |
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98 /* X [i] *= pivot ; */ |
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99 x = X [i] ; |
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100 MULT (X [i], x, pivot) ; |
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101 } |
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102 #else |
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103 BLAS_SCAL (n, pivot, X) ; |
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104 #endif |
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105 |
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106 #else |
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107 |
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108 /* -------------------------------------------------------------- */ |
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109 /* divide x by the pivot */ |
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110 /* -------------------------------------------------------------- */ |
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111 |
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112 /* This is slightly more accurate, particularly if the pivot column |
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113 * consists of only IEEE subnormals. Always do this if UMFPACK is |
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114 * being compiled as a built-in routine or mexFunction in MATLAB, |
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115 * or if gcc is being used with complex matrices. */ |
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116 |
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117 for (i = 0 ; i < n ; i++) |
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118 { |
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119 /* X [i] /= pivot ; */ |
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120 x = X [i] ; |
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121 DIV (X [i], x, pivot) ; |
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122 } |
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123 |
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124 #endif |
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125 |
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126 } |
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127 } |
