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4 | <!-- Changed by: Katsuya Amako, 4-Aug-1998 --> |
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6 | <!-- Proof read by: Joe Chuma, 14-Jun-1999 --> |
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7 | <BODY> |
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8 | <TABLE WIDTH="100%"><TR> |
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9 | <TD> |
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10 | |
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11 | |
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12 | <A HREF="index.html"> |
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13 | <IMG SRC="../../../../resources/html/IconsGIF/Contents.gif" ALT="Contents"></A> |
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14 | <IMG SRC="../../../../resources/html/IconsGIF/PreviousGR.gif" ALT="Previous"> |
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15 | <A HREF="geometryDef.html"> |
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16 | <IMG SRC="../../../../resources/html/IconsGIF/Next.gif" ALT="Next"></A> |
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17 | </TD> |
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18 | <TD ALIGN="Right"> |
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19 | <FONT SIZE="-1" COLOR="#238E23"> |
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20 | <B>Geant4 User's Guide</B> |
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21 | <BR> |
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22 | <B>For Application Developers</B> |
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23 | <BR> |
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24 | <B>Getting Started with Geant4</B> |
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25 | </FONT> |
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26 | </TD> |
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27 | </TR></TABLE> |
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28 | <BR><BR> |
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29 | |
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30 | <P ALIGN="Center"> |
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31 | <FONT SIZE="+3" COLOR="#238E23"> |
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32 | <B>2.1 How to Define the main() Program</B> |
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33 | </FONT> |
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34 | <BR><BR> |
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35 | |
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36 | <HR ALIGN="Center" SIZE="7%"> |
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37 | <p> |
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38 | |
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39 | <a name="2.1.1"> |
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40 | <H2>2.1.1 A Sample <tt>main()</tt> Method</H2></a> |
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41 | |
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42 | The contents of <tt>main()</tt> will vary according to the needs |
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43 | of a given simulation application and therefore must be supplied |
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44 | by the user. The Geant4 toolkit does not provide a <tt>main()</tt> |
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45 | method, but a sample is provided here as a guide to the beginning |
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46 | user. Source listing 2.1.1 is the simplest example of <tt>main()</tt> |
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47 | required to build a simulation program. |
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48 | <p> |
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49 | <center> |
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50 | <table border=2 cellpadding=10> |
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51 | <tr> |
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52 | <td> |
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53 | <PRE> |
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54 | #include "G4RunManager.hh" |
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55 | #include "G4UImanager.hh" |
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56 | |
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57 | #include "ExN01DetectorConstruction.hh" |
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58 | #include "ExN01PhysicsList.hh" |
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59 | #include "ExN01PrimaryGeneratorAction.hh" |
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60 | |
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61 | int main() |
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62 | { |
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63 | // construct the default run manager |
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64 | G4RunManager* runManager = new G4RunManager; |
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65 | |
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66 | // set mandatory initialization classes |
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67 | runManager->SetUserInitialization(new ExN01DetectorConstruction); |
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68 | runManager->SetUserInitialization(new ExN01PhysicsList); |
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69 | |
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70 | // set mandatory user action class |
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71 | runManager->SetUserAction(new ExN01PrimaryGeneratorAction); |
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72 | |
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73 | // initialize G4 kernel |
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74 | runManager->initialize(); |
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75 | |
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76 | // get the pointer to the UI manager and set verbosities |
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77 | G4UImanager* UI = G4UImanager::GetUIpointer(); |
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78 | UI->ApplyCommand("/run/verbose 1"); |
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79 | UI->ApplyCommand("/event/verbose 1"); |
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80 | UI->ApplyCommand("/tracking/verbose 1"); |
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81 | |
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82 | // start a run |
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83 | int numberOfEvent = 3; |
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84 | runManager->BeamOn(numberOfEvent); |
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85 | |
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86 | // job termination |
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87 | delete runManager; |
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88 | return 0; |
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89 | } |
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90 | </PRE> |
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91 | </td> |
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92 | </tr> |
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93 | <tr> |
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94 | <td align=center> |
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95 | Source listing 2.1.1<BR> |
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96 | </td> |
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97 | </tr> |
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98 | </table></center> |
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99 | <p> |
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100 | The <tt>main()</tt> method is implemented by two toolkit classes, |
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101 | <i>G4RunManager</i> and <i>G4UImanager</i>, and three classes, |
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102 | <i>ExN01DetectorConstruction</i>, <i>ExN01PhysicsList</i> and |
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103 | <i>ExN01PrimaryGeneratorAction</i>, which are derived from toolkit |
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104 | classes. Each of these are explained in the following sections. |
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105 | |
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106 | <HR> |
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107 | <a name="2.1.2"> |
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108 | <H2>2.1.2 <i>G4RunManager</i></H2></a> |
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109 | |
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110 | The first thing <tt>main()</tt> must do is create an instance of |
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111 | the <i>G4RunManager</i> class. This is the only manager class in the Geant4 |
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112 | kernel which should be explicitly constructed in the user's |
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113 | <tt>main()</tt>. It controls the flow of the program and manages the event |
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114 | loop(s) within a run. When <i>G4RunManager</i> is created, the other major |
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115 | manager classes are also created. They are deleted automatically when |
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116 | <i>G4RunManager</i> is deleted. The run manager is also responsible |
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117 | for managing initialization procedures, including methods in the user |
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118 | initialization classes. Through these the run manager must be given all |
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119 | the information necessary to build and run the simulation, including |
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120 | <OL> |
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121 | <LI>how the detector should be constructed, |
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122 | <LI>all the particles and all the physics processes to be simulated, |
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123 | <LI>how the primary particle(s) in an event should be produced and |
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124 | <LI>any additional requirements of the simulation. |
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125 | </OL> |
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126 | <p> |
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127 | In the sample <tt>main()</tt> the lines |
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128 | <pre> |
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129 | runManager->SetUserInitialization(new ExN01DetectorConstruction); |
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130 | runManager->SetUserInitialization(new ExN01PhysicsList); |
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131 | </pre> |
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132 | create objects which specify the detector geometry and physics processes, |
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133 | respectively, and pass their pointers to the run manager. |
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134 | <i>ExN01DetectorConstruction</i> is an example of a user initialization |
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135 | class which is derived from <i>G4VUserDetectorConstruction</i>. This is |
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136 | where the user describes the entire detector setup, including |
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137 | <UL> |
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138 | <LI>its geometry, |
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139 | <LI>the materials used in its construction, |
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140 | <LI>a definition of its sensitive regions and |
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141 | <LI>the readout schemes of the sensitive regions. |
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142 | </UL> |
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143 | |
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144 | Similarly <i>ExN01PhysicsList</i> is derived from <i>G4VUserPhysicsList</i> |
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145 | and requires the user to define |
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146 | <UL> |
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147 | <LI>the particles to be used in the simulation, |
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148 | <LI>the range cuts for these particles and |
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149 | <LI>all the physics processes to be simulated. |
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150 | </UL> |
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151 | |
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152 | The next instruction in <tt>main()</tt> |
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153 | <pre> |
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154 | runManager->SetUserAction(new ExN01PrimaryGeneratorAction); |
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155 | </pre> |
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156 | creates an instance of a particle generator and passes its pointer to the |
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157 | run manager. |
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158 | |
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159 | <i>ExN01PrimaryGeneratorAction</i> is an example of a user action class |
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160 | which is derived from <i>G4VUserPrimaryGeneratorAction</i>. In this class |
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161 | the user must describe the initial state of the primary event. This class |
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162 | has a public virtual method named <tt>generatePrimaries()</tt> which will |
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163 | be invoked at the beginning of each event. Details will be given in |
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164 | <a href="eventDef.html">Section 2.6</a>. Note that Geant4 does not provide |
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165 | any default behavior for generating a primary event. |
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166 | <p> |
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167 | The next instruction |
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168 | <pre> |
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169 | runManager->initialize(); |
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170 | </pre> |
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171 | performs the detector construction, creates the physics processes, calculates |
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172 | cross sections and otherwise sets up the run. The final run manager method |
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173 | in <tt>main()</tt> |
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174 | <pre> |
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175 | int numberOfEvent = 3; |
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176 | runManager->beamOn(numberOfEvent); |
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177 | </pre> |
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178 | begins a run of three sequentially processed events. The <tt>beamOn()</tt> |
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179 | method may be invoked any number of times within <tt>main()</tt> with each |
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180 | invocation representing a separate run. Once a run has begun neither the |
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181 | detector setup nor the physics processes may be changed. They may be |
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182 | changed between runs, however, as described in |
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183 | <a href="../Fundamentals/run.html#3.4.4">Section 3.4.4</a>. More information |
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184 | on <i>G4RunManager</i> in general is found in |
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185 | <a href="../Fundamentals/run.html">Section 3.4</a>. |
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186 | <p> |
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187 | As mentioned above, other manager classes are created when the run manager |
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188 | is created. One of these is the user interface manager, <i>G4UImanager</i>. |
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189 | In <tt>main()</tt> a pointer to the interface manager must be obtained |
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190 | <pre> |
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191 | G4UImanager* UI = G4UImanager::getUIpointer(); |
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192 | </pre> |
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193 | in order for the user to issue commands to the program. In the present |
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194 | example the <tt>applyCommand()</tt> method is called three times to |
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195 | direct the program to print out information at the run, event and tracking |
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196 | levels of simulation. A wide range of commands is available which allows |
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197 | the user detailed control of the simulation. A list of these commands can |
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198 | be found in <a href="../Control/commands.html">Section 7.1</a>. |
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199 | |
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200 | <HR> |
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201 | <a name="2.1.3"> |
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202 | <H2>2.1.3 User Initialization and Action Classes</H2></a> |
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203 | |
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204 | <B>Mandatory User Classes</B> |
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205 | <P> |
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206 | There are three classes which must be defined by the user. Two of them |
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207 | are user initialization classes, and the other is a user action class. |
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208 | They must be derived from the abstract base classes provided by Geant4: |
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209 | <i>G4VUserDetectorConstruction</i>, <i>G4VuserPhysicsList</i></h4> and |
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210 | <i>G4VuserPrimaryGeneratorAction</i>. Geant4 does not provide default |
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211 | behavior for these classes. <i>G4RunManager</i> checks for the existence |
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212 | of these mandatory classes when the <tt>initialize()</tt> and |
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213 | <tt>BeamOn()</tt> methods are invoked.</P> |
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214 | <P> |
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215 | As mentioned in the previous section, <i>G4VUserDetectorConstruction</i> |
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216 | requires the user to define the detector and <i>G4VUserPhysicsList</i> |
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217 | requires the user to define the physics. Detector definition will be |
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218 | discussed in Sections <a href="geometryDef.html">2.2</a> and |
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219 | <a href="materialDef.html">2.3</a>. Physics definition will be discussed |
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220 | in Sections <a href="particleDef.html">2.4</a> and |
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221 | <a href="physicsDef.html">2.5</a>. The user action class |
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222 | <i>G4VuserPrimaryGeneratorAction</i> requires that the initial event |
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223 | state be defined. Primary event generation will be discussed in |
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224 | <a href="eventDef.html">Section 2.6</a>. |
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225 | <p> |
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226 | |
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227 | <B>Optional User Action Classes</B> |
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228 | <p> |
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229 | Geant4 provides five user hook classes: |
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230 | <UL> |
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231 | <LI><i>G4UserRunAction</i> |
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232 | <LI><i>G4UserEventAction</i> |
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233 | <LI><i>G4UserStackingAction</i> |
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234 | <LI><i>G4UserTrackingAction</i> |
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235 | <LI><i>G4UserSteppingAction</i> |
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236 | </UL> |
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237 | <P> |
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238 | There are several virtual methods in each of these classes which allow the |
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239 | specification of additional procedures at all levels of the simulation |
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240 | application. Details of the user initialization and action classes are |
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241 | provided in <a href="../UserActions/index.html">Section 6</a>. |
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242 | |
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243 | <HR> |
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244 | <a name="2.1.4"> |
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245 | <H2>2.1.4. <i>G4UImanager</i> and UI Command Submission</H2></a> |
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246 | |
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247 | Geant4 provides a category named <b>intercoms</b>. <i>G4UImanager</i> |
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248 | is the manager class of this category. Using the functionalities of this |
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249 | category, you can invoke <b>set</b> methods of class objects of which you |
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250 | do not know the pointer. In Source listing 2.1.1, the verbosities of various |
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251 | Geant4 manager classes are set. Detailed mechanism description and usage of |
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252 | <b>intercoms</b> will be given in the next chapter, with a list of available |
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253 | commands. Command submission can be done all through the application. |
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254 | <p> |
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255 | <center> |
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256 | <table border=2 cellpadding=10> |
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257 | <tr> |
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258 | <td> |
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259 | <PRE> |
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260 | #include "G4RunManager.hh" |
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261 | #include "G4UImanager.hh" |
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262 | <font color="#0000ff">#include "G4UIterminal.hh"</font> |
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263 | #include "G4VisExecutive.hh" |
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264 | |
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265 | #include "N02DetectorConstruction.hh" |
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266 | #include "N02PhysicsList.hh" |
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267 | #include "N02PrimaryGeneratorAction.hh" |
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268 | #include "N02RunAction.hh" |
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269 | #include "N02EventAction.hh" |
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270 | #include "N02SteppingAction.hh" |
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271 | |
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272 | #include "g4templates.hh" |
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273 | |
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274 | int main(int argc,char** argv) |
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275 | { |
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276 | // construct the default run manager |
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277 | G4RunManager * runManager = new G4RunManager; |
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278 | |
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279 | // set mandatory initialization classes |
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280 | N02DetectorConstruction* detector = new N02DetectorConstruction; |
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281 | runManager->SetUserInitialization(detector); |
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282 | runManager->SetUserInitialization(new N02PhysicsList); |
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283 | |
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284 | // visualization manager |
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285 | G4VisManager* visManager = new G4VisExecutive; |
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286 | visManager->initialize(); |
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287 | |
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288 | // set user action classes |
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289 | runManager->SetUserAction(new N02PrimaryGeneratorAction(detector)); |
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290 | runManager->SetUserAction(new N02RunAction); |
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291 | runManager->SetUserAction(new N02EventAction); |
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292 | runManager->SetUserAction(new N02SteppingAction); |
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293 | |
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294 | // get the pointer to the User Interface manager |
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295 | G4UImanager* UI = G4UImanager::GetUIpointer(); |
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296 | |
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297 | <font color="#0000ff"> if(argc==1) |
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298 | // Define (G)UI terminal for interactive mode |
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299 | { |
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300 | G4UIsession * session = new G4UIterminal; |
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301 | UI->ApplyCommand("/control/execute prerun.g4mac"); |
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302 | session->sessionStart(); |
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303 | delete session; |
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304 | } |
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305 | else |
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306 | // Batch mode |
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307 | { |
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308 | G4String command = "/control/execute "; |
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309 | G4String fileName = argv[1]; |
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310 | UI->ApplyCommand(command+fileName); |
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311 | }</font> |
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312 | |
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313 | // job termination |
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314 | delete visManager; |
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315 | delete runManager; |
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316 | |
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317 | return 0; |
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318 | } |
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319 | </pre> |
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320 | </td> |
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321 | </tr> |
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322 | <tr> |
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323 | <td align=center> |
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324 | Source list 2.1.2<br> |
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325 | An example of <tt>main()</tt> using interactive |
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326 | terminal and visualization. Code modified from 2.1.1. are shown in blue. |
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327 | </td> |
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328 | </tr> |
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329 | </table></center> |
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330 | <p> |
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331 | |
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332 | <HR> |
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333 | <a name="2.1.5"> |
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334 | <H2>2.1.5 <i>G4cout</i> and <i>G4cerr</i></H2></a> |
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335 | |
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336 | Although not yet included in the above examples, output streams will be |
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337 | needed. <i>G4cout</i> and <i>G4cerr</i> are <b>iostream</b> objects defined |
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338 | by Geant4. The usage of these objects is exactly the same as the ordinary |
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339 | <i>cout</i> and <i>cerr</i>, except that the output streams will be handled by |
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340 | <i>G4UImanager</i>. Thus, output strings may be displayed on another window |
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341 | or stored in a file. Manipulation of these output streams will be described |
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342 | in <a href="../Control/userInterfaceCommand.html#7.2.4">Section 7.2.4</a>. |
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343 | These objects should be used instead of the ordinary <i>cout</i> and |
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344 | <i>cerr</i>. |
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345 | <P> |
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346 | <HR> |
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347 | <A HREF="../../../../Authors/html/subjectsToAuthors.html"> |
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348 | <I>About the authors</I></A> |
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349 | </BODY> |
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350 | </HTML> |
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