1 | #ifndef __HALTON_H
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2 | #define __HALTON_H
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3 |
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4 | #include <iostream>
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5 |
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6 | namespace GtpVisibilityPreprocessor {
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7 |
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8 |
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9 | /**
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10 | * Assert whether the argument is a prime number.
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11 | * @param number the number to be checked
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12 | */
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13 | inline bool IsPrime(const int number) {
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14 | bool isIt = true;
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15 | for(int i = 2; i < number; i++) {
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16 | if(number % i == 0) {
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17 | isIt = false;
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18 | break;
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19 | }
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20 | }
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21 | if(number == 2) {
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22 | isIt = false;
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23 | }
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24 | return isIt;
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25 | }
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26 |
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27 |
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28 | /**
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29 | * Find the nth prime number.
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30 | * @param index the ordinal position in the sequence
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31 | */
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32 | inline int FindPrime(const int index) {
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33 | // if (index < 1) {
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34 | // cerr<<"FindPrime: The argument must be non-negative."<<endl;
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35 | // return -1;
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36 | // }
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37 |
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38 | const int primes[] = {-1, 1, 3, 5, 7, 11, 13};
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39 | if (index <= 6)
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40 | return primes[index];
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41 |
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42 | int prime = 1;
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43 | int found = 1;
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44 | while(found != index) {
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45 | prime += 2;
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46 | if(IsPrime(prime) == true) {
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47 | found++;
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48 | }
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49 | }
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50 | return prime;
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51 | }
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52 |
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53 |
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54 | inline float halton(float baseRec, float prev) {
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55 | // float r = 1 - prev - 1e-10f;
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56 | float r = 1.0f - prev;
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57 | //float r = 1.0f - prev;
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58 | if (baseRec < r)
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59 | return prev + baseRec;
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60 | float h = baseRec;
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61 | float hh;
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62 | do {
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63 | hh = h;
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64 | h *= baseRec;
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65 | } while (h > r);
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66 | return prev + hh + h - 1.0f;
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67 | }
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68 |
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69 | template<int T>
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70 | struct Halton {
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71 | static float _invBases[T];
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72 | float _prev[T];
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73 |
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74 | public:
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75 |
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76 | void Reset() {
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77 | for (int i=0; i < T; i++)
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78 | _prev[i] = 0;
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79 | }
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80 |
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81 | Halton(const bool initializeBases) {
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82 | for (int i=0; i < T; i++) {
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83 | int base = FindPrime(i+1);
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84 | if (base == 1)
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85 | base++;
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86 | _invBases[i] = 1.0f/base;
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87 | }
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88 | }
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89 |
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90 | Halton() {
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91 | Reset();
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92 | }
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93 |
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94 | void
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95 | GetNext(float *a) {
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96 | for (int i=0; i < T; i++) {
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97 | a[i] = halton(_invBases[i], _prev[i]);
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98 | _prev[i] = a[i];
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99 | }
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100 | }
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101 |
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102 | };
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103 |
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104 | struct Halton2 {
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105 | static float _invBases[2];
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106 | float _prev[2];
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107 |
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108 | public:
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109 |
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110 | void Reset() {
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111 | _prev[0] =_prev[1] = 0;
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112 | }
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113 |
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114 | Halton2() {
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115 | _invBases[0] = 1.0f/2;
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116 | _invBases[1] = 1.0f/3;
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117 | Reset();
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118 | }
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119 |
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120 | void
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121 | GetNext(float &a, float &b) {
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122 | a = halton(_invBases[0], _prev[0]);
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123 | b = halton(_invBases[1], _prev[1]);
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124 | _prev[0] = a;
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125 | _prev[1] = b;
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126 | }
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127 | };
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128 |
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129 |
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130 |
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131 | struct HaltonSequence {
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132 | public:
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133 | int index;
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134 |
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135 | static int sPregeneratedDim;
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136 | static int sPregeneratedNumber;
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137 | static float *sPregeneratedValues;
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138 |
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139 | // special construtor for pregenerating static halton sequences
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140 | HaltonSequence(const int dim,
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141 | const int number);
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142 |
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143 | HaltonSequence():index(1) {}
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144 |
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145 | void Reset() {
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146 | index = 1;
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147 | }
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148 |
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149 | void
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150 | GetNext(const int dimensions, float *p);
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151 |
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152 | void GenerateNext() {
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153 | index++;
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154 | }
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155 |
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156 | double GetNumber(const int dimension) {
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157 | int base = FindPrime(dimension);
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158 | if(base == 1) {
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159 | base++; //The first dimension uses base 2.
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160 | }
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161 |
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162 | int _p1 = base;
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163 | float _ip1 = 1.0f/base;
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164 | float p, u=0.0f;
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165 | int kk, a;
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166 |
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167 | // the first coordinate
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168 | for (p = _ip1, kk = index ; kk ; p *= _ip1, kk /= _p1)
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169 | if ((a = kk % _p1))
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170 | u += a * p;
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171 |
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172 | return u;
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173 | }
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174 |
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175 | /**
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176 | * Returns the nth number in the sequence, taken from a specified dimension.
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177 | * @param index the ordinal position in the sequence
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178 | * @param dimension the dimension
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179 | */
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180 |
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181 | double GetNumberOld(const int dimension) {
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182 | int base = FindPrime(dimension);
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183 | if(base == 1) {
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184 | base++; //The first dimension uses base 2.
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185 | }
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186 | double remainder;
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187 | double output = 0.0;
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188 | double fraction = 1.0 / (double)base;
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189 | int N1 = 0;
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190 | int copyOfIndex = index;
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191 | if((base >= 2) && (index >= 1)) {
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192 | while(copyOfIndex > 0) {
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193 | N1 = (copyOfIndex / base);
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194 | remainder = copyOfIndex % base;
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195 | output += fraction * remainder;
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196 | copyOfIndex = (int)(copyOfIndex / base);
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197 | fraction /= (double)base;
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198 | }
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199 | return output;
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200 | }
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201 | else {
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202 | std::cerr<<"Error generating Halton sequence."<<std::endl;
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203 | exit(1);
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204 | }
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205 | }
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206 | };
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207 |
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208 | extern Halton2 halton2;
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209 | }
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210 |
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211 | #endif
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