1 | \chapter{Global Usage} |
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2 | |
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3 | \section{Design Philosophy} |
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4 | The global category covers the system of units, constants, numerics and |
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5 | random number handling. It can be considered a place-holder for |
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6 | "general purpose" classes used by all categories defined in {\sc Geant4}. |
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7 | No back-dependencies to other {\sc Geant4} categories affect the "global" |
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8 | domain. There are direct dependencies of the global category on external |
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9 | packages, such as CLHEP, STL, and miscellaneous system utilities. |
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10 | |
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11 | Within the management sub-category are ``utility'' classes generally used |
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12 | within the {\sc Geant4} kernel. They are, for the most part, uncorrelated |
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13 | with one another and include: |
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14 | \begin{itemize} |
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15 | \item {\it G4Allocator} |
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16 | \item {\it G4FastVector} |
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17 | \item {\it G4ReferenceCountedHandle} |
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18 | \item {\it G4PhysicsVector, G4LPhysicsFreeVector, G4PhysicsOrderedFreeVector} |
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19 | \item {\it G4Timer} |
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20 | \item {\it G4UserLimits} |
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21 | \item {\it G4UnitsTable} |
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22 | \end{itemize} |
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23 | A general description of these classes is given in section 3.2 of the |
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24 | {\sc Geant4} User's Guide for Application Developers. |
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25 | |
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26 | In applications where it is necessary to generate random numbers (normally |
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27 | from the same engine) in many different methods and parts of the program, it |
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28 | is highly desirable not to rely on or require knowledge of the global objects |
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29 | instantiated. By using static methods via a unique generator, the randomness |
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30 | of a sequence of numbers is best assured. Hence the use of a static generator |
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31 | has been introduced in the original design of HEPRandom as a project |
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32 | requirement in {\sc Geant4}. |
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33 | |
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34 | \section{Class Design} |
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35 | |
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36 | Analysis and design of the HEPRandom module have been achieved following |
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37 | the Booch Object-Oriented methodology. Some of the original design |
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38 | diagrams in Booch notation are reported below. Fig. \ref{figure:random-1} |
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39 | is a general picture of the static class diagram. |
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40 | |
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41 | \begin{itemize} |
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42 | \item {\bf HepRandomEngine} - |
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43 | abstract class defining the interface for each Random engine. Its pure |
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44 | virtual methods must be defined by its subclasses representing the |
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45 | concrete Random engines. |
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46 | \item {\bf HepJamesRandom} - |
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47 | class inheriting from HepRandomEngine and defining a flat random number |
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48 | generator according to the algorithm described in |
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49 | "F.James, Comp.Phys.Comm. 60 (1990) 329". This class is instantiated by |
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50 | default as the default random engine. |
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51 | \item {\bf DRand48Engine} - |
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52 | class inheriting from HepRandomEngine and defining a flat random number |
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53 | generator according to the drand48() and srand48() system functions from |
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54 | the C standard library. |
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55 | \item {\bf RandEngine} - |
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56 | class inheriting from HepRandomEngine and defining a flat random number |
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57 | generator according to the rand() and srand() system functions from the |
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58 | C standard library. |
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59 | \item {\bf RanluxEngine} - |
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60 | class inheriting from HepRandomEngine and defining a flat random number |
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61 | generator according to the algorithm described in |
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62 | "F.James, Comp.Phys.Comm. 60 (1990) 329-344" and originally implemented |
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63 | in FORTRAN 77 as part of the MATHLIB HEP library. It provides 5 different |
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64 | "luxury" levels [0..4]. |
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65 | \item {\bf RanecuEngine} - |
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66 | class inheriting from HepRandomEngine and defining a flat random number |
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67 | generator according to the algorithm RANECU originally written in |
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68 | FORTRAN 77 as part of the MATHLIB HEP library. It uses a table of seeds |
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69 | which provides uncorrelated couples of seed values. |
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70 | \item {\bf HepRandom} - |
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71 | the main class collecting all the methods defining the different random |
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72 | generators applied to HepRandomEngine. It is a singleton class which all |
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73 | the distribution classes derive from. This singleton is instantiated by |
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74 | default. |
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75 | \item {\bf RandFlat} - |
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76 | distribution class for flat random number generation. It also provides |
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77 | methods to fill an array of flat random values, given its size or shoot |
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78 | bits. |
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79 | \item {\bf RandExponential} - |
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80 | distribution class defining exponential random number distribution, given |
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81 | a mean. It also provides a method to fill an array of flat random values, |
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82 | given its size. |
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83 | \item {\bf RandGauss} - |
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84 | distribution class defining Gauss random number distribution, given a |
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85 | mean or specifying also a deviation. It also provides a method to fill |
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86 | an array of flat random values, given its size. |
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87 | \item {\bf RandBreitWigner} - |
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88 | distribution class defining the Breit-Wigner random number distribution. |
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89 | It also provides a method to fill an array of flat random values, given |
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90 | its size. |
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91 | \item {\bf RandPoisson} - |
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92 | distribution class defining Poisson random number distribution, given a |
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93 | mean. It also provides a method to fill an array of flat random values, |
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94 | given its size. |
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95 | \end{itemize} |
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96 | |
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97 | |
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98 | \begin{figure}[h!] |
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99 | \includegraphics[angle=0,scale=0.6]{OOAnalysisDesign/GlobalUsage/classDgmRandom.eps} |
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100 | \vspace{10pt} |
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101 | \caption{HEPRandom module} |
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102 | \label{figure:random-1} |
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103 | \end{figure} |
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104 | |
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105 | |
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106 | Fig. \ref{figure:random-2} is a dynamic object diagram illustrating the |
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107 | situation when a single random number is thrown by the static generator |
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108 | according to one of the available distributions. Only one engine is |
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109 | assumed to active at a time. |
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110 | |
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111 | \begin{figure}[h!] |
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112 | \includegraphics[angle=0,scale=0.6]{OOAnalysisDesign/GlobalUsage/ObjDiagStat.eps} |
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113 | \vspace{10pt} |
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114 | \caption{Shooting via the generator} |
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115 | \label{figure:random-2} |
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116 | \end{figure} |
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117 | |
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118 | Fig. \ref{figure:random-3} illustrates a random number being thrown by |
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119 | explicitly specifying an engine which can be shared by many distribution |
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120 | objects. The static interface is skipped here. |
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121 | |
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122 | \begin{figure}[h!] |
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123 | \includegraphics[angle=0,scale=0.6]{OOAnalysisDesign/GlobalUsage/ObjDiagDist.eps} |
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124 | \vspace{10pt} |
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125 | \caption{Shooting via distribution objects} |
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126 | \label{figure:random-3} |
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127 | \end{figure} |
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128 | |
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129 | Fig. \ref{figure:random-4} illustrates the situation when many generators are |
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130 | defined, each by a distribution and an engine. The static interface is |
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131 | skipped here. |
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132 | |
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133 | \begin{figure}[h!] |
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134 | \includegraphics[angle=0,scale=0.6]{OOAnalysisDesign/GlobalUsage/ObjDiagEng.eps} |
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135 | \vspace{10pt} |
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136 | \caption{Shooting with arbitrary engines} |
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137 | \label{figure:random-4} |
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138 | \end{figure} |
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139 | |
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140 | For detailed documentation about the HEPRandom classes see the |
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141 | CLHEP Reference Guide\newline |
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142 | (http://cern.ch/clhep/manual/RefGuide)\newline |
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143 | or the CLHEP User Manual\newline |
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144 | (http://cern.ch/clhep/manual/UserGuide).\newline |
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145 | Informations written in this manual are extracted |
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146 | from the original manifesto distributed with the HEPRandom package\newline |
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147 | (http://cern.ch/clhep/manual/UserGuide/Random/Random.html). |
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148 | |
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149 | \paragraph{HEPNumerics} |
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150 | The HEPNumerics module includes a set of classes which implement numerical |
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151 | algorithms for general use in {\sc Geant4}. Section 3.2.3 of the User's Guide |
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152 | for Application Developers contains a description of each class. Most of |
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153 | the algorithms were implemented using methods from the following books: |
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154 | \mbox{} |
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155 | \begin{itemize} |
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156 | \item B.H. Flowers, "An introduction to Numerical Methods In C++", |
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157 | Claredon Press, Oxford 1995. |
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158 | \item M. Abramowitz, I. Stegun, "Handbook of mathematical functions", |
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159 | DOVER Publications INC, New York 1965 ; chapters 9, 10, and 22. |
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160 | \end{itemize} |
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161 | |
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162 | \paragraph{HEPGeometry} |
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163 | Documentation for the HEPGeometry module is provided in the CLHEP |
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164 | Reference Guide\newline |
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165 | (http://cern.ch/clhep/manual/RefGuide) |
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166 | or the CLHEP User Manual\newline |
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167 | (http://cern.ch/clhep/manual/UserGuide) |
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168 | |
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169 | \section{Status of this chapter} |
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170 | |
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171 | 01.12.02 minor update by G. Cosmo \\ |
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172 | 18.06.05 introductory paragraphs added and minor grammar changes by D.H. Wright \\ |
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