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| 3 | <title>Usecases of importance sampling and scoring in Geant4</title><meta name="generator" content="DocBook XSL Stylesheets V1.51.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book"><div class="titlepage"><div><h1 class="title"><a name="BiasScoreIssues"></a>Usecases of importance sampling and scoring in Geant4</h1></div><div><div class="author"><h3 class="author">Michael Dressel</h3></div></div><hr></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt>1. <a href="#introduction">Introduction</a></dt><dt>2. <a href="#mass">Mass-geometry</a></dt><dd><dl><dt>2.1. <a href="#mass-parent-ms">Particle suffers multiple scattering</a></dt><dt>2.2. <a href="#mass-parent-zero">Parent particle suffers process on mass-boundary</a></dt><dt>2.3. <a href="#mass-phys-daughter">Daughter created by a physics process on boundary</a></dt><dt>2.4. <a href="#mass-bias-daughter">Daughter created by biasing</a></dt></dl></dd><dt>3. <a href="#parallel">Parallel-geometry</a></dt><dd><dl><dt>3.1. <a href="#parallel-parent">Particle suffers multiple scattering.</a></dt><dt>3.2. <a href="#parallel-parent-zero">Particle suffers physics process on boundary</a></dt><dt>3.3. <a href="#parallel-phys-daughter">Daughter created by a physics process on a boundary</a></dt><dt>3.4. <a href="#parallel-bias-daughter">Daughter created by biasing</a></dt></dl></dd><dt>4. <a href="#problems">To the problematic usecases</a></dt><dt>5. <a href="#summary">Summary</a></dt></dl></div><div class="chapter"><div class="titlepage"><div><h2 class="title"><a name="introduction"></a>Chapter 1. Introduction</h2></div></div><p>This document should provide a list of |
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| 4 | usecases to check the behaviour of importance sampling and scoring |
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| 5 | against. A distinction is made between sampling in a mass and |
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| 6 | parallel geometry.</p><p><a href="#mass" title="Chapter 2. Mass-geometry">Chapter 2</a> and <a href="#parallel" title="Chapter 3. Parallel-geometry">Chapter 3</a> |
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| 7 | give detailed usecase descriptions.</p><p><a href="#problems" title="Chapter 4. To the problematic usecases">Chapter 4</a> sum's up the problematic usecases |
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| 8 | and their possible solutions.</p><p><a href="#summary" title="Chapter 5. Summary">Chapter 5</a> contains the summary.</p></div><div class="chapter"><div class="titlepage"><div><h2 class="title"><a name="mass"></a>Chapter 2. Mass-geometry</h2></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt>2.1. <a href="#mass-parent-ms">Particle suffers multiple scattering</a></dt><dt>2.2. <a href="#mass-parent-zero">Parent particle suffers process on mass-boundary</a></dt><dt>2.3. <a href="#mass-phys-daughter">Daughter created by a physics process on boundary</a></dt><dt>2.4. <a href="#mass-bias-daughter">Daughter created by biasing</a></dt></dl></div><div class="sect1"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="mass-parent-ms"></a>2.1. Particle suffers multiple scattering</h2></div></div><div class="variablelist"><dl><dt><span class="term"><span class="emphasis"><em>Description:</em></span></span></dt><dd><p>A particle step reaches a boundary between volume <span class="emphasis"><em> |
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| 9 | A</em></span> and <span class="emphasis"><em>B</em></span> |
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| 10 | of the mass geometry and it's momentum is changed by a multiple |
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| 11 | scattering process.</p></dd><dt><span class="term"><span class="emphasis"><em>Relevance:</em></span></span></dt><dd><p>Multiple scatteing applies for charged particles. |
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| 12 | The current version is not intended to be used for charged particles but |
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| 13 | future versions will.</p></dd><dt><span class="term"><span class="emphasis"><em>Figure:</em></span></span></dt><dd><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0"><tr><td><img src="figures/mass-parent.gif" alt="Parent particle"></td></tr></table><div class="caption"><p>A particle crosses the boundary in the mass |
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| 14 | geometry. The momentum is changed by multiple scattering.</p></div></div></dd><dt><span class="term"><span class="emphasis"><em>Detailed description:</em></span></span></dt><dd><p>Three steps <span class="emphasis"><em>1</em></span>, <span class="emphasis"><em>2</em></span>, |
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| 15 | <span class="emphasis"><em>3</em></span> occur:</p><div class="orderedlist"><ol type="1"><li><p><a name="parent-step-1"></a>'st step:</p><div class="orderedlist"><ol type="a"><li><p>Step one is limited by the transportation. The |
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| 16 | transportation moves the particle on the boundary and locates it |
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| 17 | in volume <span class="emphasis"><em>B</em></span>.</p></li><li><p>Biasing split's or deletes the particle |
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| 18 | and changes weight correctly. |
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| 19 | See also: <a href="#mass-bias-daughter" title="2.4. Daughter created by biasing">Section 2.4</a></p></li><li><p>Scoring counts the track as entering volume |
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| 20 | <span class="emphasis"><em>B</em></span></p></li><li><p>Multiple scattering changes |
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| 21 | the momentum to point back in volume <span class="emphasis"><em>A</em></span> again.</p></li></ol></div></li><li><p>'nd step:</p><div class="orderedlist"><ol type="a"><li><p>Transportation limits step. Transportation |
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| 22 | locates particle in volume <span class="emphasis"><em>A</em></span>.</p></li><li><p>Biasing split's or deletes the particle and changes |
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| 23 | weight correctly. |
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| 24 | See also: <a href="#mass-bias-daughter" title="2.4. Daughter created by biasing">Section 2.4</a></p></li><li><p>Scoring counts the track as entering volume |
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| 25 | <span class="emphasis"><em>A</em></span></p></li></ol></div></li><li><p>'rd step:</p><p>Step may be limited by any process.</p><p>Transportation locates particle at the new |
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| 26 | position </p></li></ol></div></dd><dt><span class="term"><span class="emphasis"><em>Comment:</em></span></span></dt><dd><p> |
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| 27 | Multiple scattering is related to volume <span class="emphasis"><em>A</em></span> therefore |
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| 28 | the following should be considered:</p><div class="itemizedlist"><ul type="disc"><li><p> |
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| 29 | Importance sampling should neither run in the first nor in the second |
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| 30 | step. |
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| 31 | </p></li><li><p> |
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| 32 | The particle should not be scored as entering volume |
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| 33 | <span class="emphasis"><em>B</em></span> in the first step and it should not be scored as |
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| 34 | entering <span class="emphasis"><em>A</em></span> in the second step. |
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| 35 | </p></li></ul></div></dd></dl></div></div><div class="sect1"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="mass-parent-zero"></a>2.2. Parent particle suffers process on mass-boundary</h2></div></div><div class="variablelist"><dl><dt><span class="term"><span class="emphasis"><em>Description:</em></span></span></dt><dd><p>A particle step reaches a boundary between volume <span class="emphasis"><em> |
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| 36 | A</em></span> and <span class="emphasis"><em>B</em></span> |
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| 37 | of the mass geometry. It is located in volume |
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| 38 | <span class="emphasis"><em>B</em></span>. Then a process returns a zero step length, |
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| 39 | get's called and changes the momentum back to <span class="emphasis"><em> |
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| 40 | A</em></span>.</p></dd><dt><span class="term"><span class="emphasis"><em>Relevance:</em></span></span></dt><dd><p> |
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| 41 | A process should never return step length = 0. |
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| 42 | But the situation applies also if a process proposes a step length so |
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| 43 | small that the track is located within a distance of kCarTolerance to the |
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| 44 | boundary. |
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| 45 | </p></dd><dt><span class="term"><span class="emphasis"><em>Figure:</em></span></span></dt><dd><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0"><tr><td><img src="figures/mass-parent-zero.gif" alt="Parent particle suffers a process on mass-boundary"></td></tr></table><div class="caption"><p>A particle crosses the boundary in the mass |
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| 46 | geometry. The momentum is changed by a process that returned sl=0.</p></div></div></dd><dt><span class="term"><span class="emphasis"><em>Detailed description:</em></span></span></dt><dd><p>Three steps <span class="emphasis"><em>1</em></span>, <span class="emphasis"><em>2</em></span>, |
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| 47 | <span class="emphasis"><em>3</em></span> occur:</p><div class="orderedlist"><ol type="1"><li><p><a name="parent-step-zero-1"></a>step</p><div class="orderedlist"><ol type="a"><li><p>Step one is limited by the transportation. The |
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| 48 | transportation moves the particle on the boundary and locates it |
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| 49 | in volume <span class="emphasis"><em>B</em></span>.</p></li><li><p>Biasing split's or deletes the particle |
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| 50 | and changes weight correctly. |
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| 51 | See also: <a href="#mass-bias-daughter" title="2.4. Daughter created by biasing">Section 2.4</a></p></li><li><p>Scoring counts the track as entering volume |
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| 52 | <span class="emphasis"><em>B</em></span></p></li></ol></div></li><li><p>step</p><div class="orderedlist"><ol type="a"><li><p>A process returns step length = 0.</p></li><li><p>Scoring may count a collision with the |
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| 53 | correct weight according to volume <span class="emphasis"><em>B</em></span>.</p></li><li><p>The process changes the particles momentum, |
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| 54 | and may create daughter particles. (See |
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| 55 | <a href="#mass-phys-daughter" title="2.3. Daughter created by a physics process on boundary">Section 2.3</a>) </p></li></ol></div></li><li><p>step</p><div class="orderedlist"><ol type="a"><li><p>The step is limited by transportation. |
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| 56 | Transportation locates the particle in volume<span class="emphasis"><em>A</em></span>. |
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| 57 | </p></li><li><p>Biasing may delete the particle and change weight. |
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| 58 | </p></li><li><p>Scoring counts the track as entering volume |
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| 59 | <span class="emphasis"><em>A</em></span></p></li></ol></div></li></ol></div></dd><dt><span class="term"><span class="emphasis"><em>Comment:</em></span></span></dt><dd><p>This way the particle is treated correctly. |
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| 60 | </p></dd></dl></div></div><div class="sect1"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="mass-phys-daughter"></a>2.3. Daughter created by a physics process on boundary</h2></div></div><div class="variablelist"><dl><dt><span class="term"><span class="emphasis"><em>Description:</em></span></span></dt><dd><p>A particle step reaches a boundary in the mass geometry |
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| 61 | between volume |
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| 62 | <span class="emphasis"><em>A</em></span> and volume <span class="emphasis"><em>B</em></span>. A physical |
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| 63 | process returns steplength =0 and creates a daughter.</p></dd><dt><span class="term"><span class="emphasis"><em>Relevance:</em></span></span></dt><dd><p> |
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| 64 | A process should never return step length = 0. |
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| 65 | But the situation applies also if a process proposes a step length so |
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| 66 | small that the track is located within a distance of kCarTolerance to the |
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| 67 | boundary. |
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| 68 | </p></dd><dt><span class="term"><span class="emphasis"><em>Figure:</em></span></span></dt><dd><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0"><tr><td><img src="figures/mass-phys-daughter-zero.gif" alt="A process creates a daughter on the boundary."></td></tr></table><div class="caption"><p>A process creates a daughter on the boundary.</p></div></div></dd><dt><span class="term"><span class="emphasis"><em>Detailed description:</em></span></span></dt><dd><p>The description of |
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| 69 | two steps of the particle and the first step of |
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| 70 | the daughter created by a physical process on the boundary:</p><div class="orderedlist"><ol type="1"><li><p><span class="emphasis"><em>Cross boundary.</em></span></p><p>This is equivalent to step one in |
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| 71 | <a href="#mass-parent-zero" title="2.2. Parent particle suffers process on mass-boundary">Section 2.2</a></p></li><li><p><span class="emphasis"><em>Physics process.</em></span></p><div class="orderedlist"><ol type="a"><li><p>A physics process returns step length = 0.</p></li><li><p>Scoring may count collsision with the original |
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| 72 | track momentum and the correct weight.</p></li><li><p>The physics process changes the momentum of the |
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| 73 | particle and creates a daughter with momentum pointing to |
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| 74 | volume <span class="emphasis"><em>A</em></span>.</p></li></ol></div></li><li><p> |
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| 75 | First step <span class="emphasis"><em>1.d</em></span> of daughter</p><p><span class="strong"><em>The daughter should be |
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| 76 | located in volume</em></span> <span class="emphasis"><em>B</em></span> |
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| 77 | <span class="strong"><em> inspide of having it's momentum pointing |
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| 78 | to volume </em></span><span class="emphasis"><em>A</em></span> !</p><p> In this mass geometry case it should be done correct by |
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| 79 | the transportation since the Touchable of the doughter |
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| 80 | can be taken into account for location. |
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| 81 | </p></li></ol></div></dd><dt><span class="term"><span class="emphasis"><em>Comment:</em></span></span></dt><dd><p> |
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| 82 | If the daughter particle is located in volume <span class="emphasis"><em>B</em></span> |
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| 83 | the situation should be treated correctly. |
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| 84 | </p></dd></dl></div></div><div class="sect1"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="mass-bias-daughter"></a>2.4. Daughter created by biasing</h2></div></div><div class="variablelist"><dl><dt><span class="term"><span class="emphasis"><em>Description:</em></span></span></dt><dd><p>A parent particle crosses the boundary in the mass |
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| 85 | geometry. Biasing creates copies of the particle. |
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| 86 | </p></dd><dt><span class="term"><span class="emphasis"><em>Relevance:</em></span></span></dt><dd><p> |
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| 87 | The most likely situation if a particle corsses a boundary and the |
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| 88 | importance of the enterung volume is higher then the importance |
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| 89 | of the exitiong volume. |
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| 90 | </p></dd><dt><span class="term"><span class="emphasis"><em>Figure:</em></span></span></dt><dd><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0"><tr><td><img src="figures/mass-bias-daughter.gif" alt="A daughter created by biasing"></td></tr></table><div class="caption"><p>A particle crosses the boundary in the mass |
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| 91 | geometry. Biasing creates a daughter.</p></div></div></dd><dt><span class="term"><span class="emphasis"><em>Detailed description:</em></span></span></dt><dd><p>A step <span class="emphasis"><em>1</em></span> of the parent and the |
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| 92 | first step <span class="emphasis"><em>1.d</em></span> are shown:</p><div class="orderedlist"><ol type="1"><li><p><span class="emphasis"><em>parent step</em></span></p><div class="orderedlist"><ol type="a"><li><p>Step one is limited by the transportation. The |
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| 93 | transportation moves the particle on the boundary and locates it |
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| 94 | in volume <span class="emphasis"><em>B</em></span>.</p></li><li><p>Biasing split's or deletes the particle |
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| 95 | and changes weight correctly.</p></li><li><p>Scoring counts the track as entering volume |
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| 96 | <span class="emphasis"><em>B</em></span></p></li></ol></div></li><li><p><span class="emphasis"><em>1.d: first step of daughter</em></span></p><div class="orderedlist"><ol type="a"><li><p>G4 locates the daughter |
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| 97 | in <span class="emphasis"><em>B</em></span>.</p></li><li><p>Any process may limit the step.</p></li></ol></div></li></ol></div></dd><dt><span class="term"><span class="emphasis"><em>Comment:</em></span></span></dt><dd><p> |
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| 98 | This should be the coorect treatment of the daughter particle created by |
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| 99 | importance sampling. |
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| 100 | </p></dd></dl></div></div></div><div class="chapter"><div class="titlepage"><div><h2 class="title"><a name="parallel"></a>Chapter 3. Parallel-geometry</h2></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt>3.1. <a href="#parallel-parent">Particle suffers multiple scattering.</a></dt><dt>3.2. <a href="#parallel-parent-zero">Particle suffers physics process on boundary</a></dt><dt>3.3. <a href="#parallel-phys-daughter">Daughter created by a physics process on a boundary</a></dt><dt>3.4. <a href="#parallel-bias-daughter">Daughter created by biasing</a></dt></dl></div><div class="sect1"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="parallel-parent"></a>3.1. Particle suffers multiple scattering.</h2></div></div><div class="variablelist"><dl><dt><span class="term"><span class="emphasis"><em>Description:</em></span></span></dt><dd><p>A particle step is limited by a boundary in the parallel |
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| 101 | geometry between volumes <span class="emphasis"><em>A</em></span> and |
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| 102 | <span class="emphasis"><em>B</em></span>. |
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| 103 | Multiple scattering occures.</p></dd><dt><span class="term"><span class="emphasis"><em>Relevance:</em></span></span></dt><dd><p> |
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| 104 | Multiple scatteing applies for charged particles. |
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| 105 | The current version is not intended to be used for charged particles but |
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| 106 | future versions will. |
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| 107 | </p></dd><dt><span class="term"><span class="emphasis"><em>Figure:</em></span></span></dt><dd><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0"><tr><td><img src="figures/parallel-parent.gif" alt="Parent particle"></td></tr></table><div class="caption"><p>A particle crosses the boundary in the parallel |
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| 108 | geometry. The momentum is changed by multiple scattering.</p></div></div></dd><dt><span class="term"><span class="emphasis"><em>Detailed description:</em></span></span></dt><dd><p>Three steps <span class="emphasis"><em>1</em></span>, <span class="emphasis"><em>2</em></span>, |
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| 109 | <span class="emphasis"><em>3</em></span> occur:</p><div class="orderedlist"><ol type="1"><li><p><a name="parallel-parent-step-1"></a>Step:</p><div class="orderedlist"><ol type="a"><li><p>The step is limited by a boundary in the parallel |
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| 110 | geometry found by the ParallelImportanceProcess.</p></li><li><p>Transportation moves the particle in the mass |
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| 111 | geometry.</p></li><li><p>The ParallelImportanceProcess |
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| 112 | moves the particle on the boundary and locates it |
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| 113 | in volume <span class="emphasis"><em>B</em></span> of the parallel geometry. |
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| 114 | Biasing splits or plays Russian Roulette and changes the weight.</p><p>The ParallelImportanceProcess may create daughters |
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| 115 | see <a href="#parallel-bias-daughter" title="3.4. Daughter created by biasing">Section 3.4</a></p></li><li><p>Scoring counts a track entering.</p></li><li><p>Multiple scattering changes the momentum of the |
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| 116 | particle.</p></li></ol></div></li><li><p>Step:</p><div class="orderedlist"><ol type="a"><li><p>The step is limited by the boundary in the |
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| 117 | parallel geometry found by the ParallelImportanceProcess.</p></li><li><p>Biasing split's or deletes the particle and |
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| 118 | changes weight correctly.</p></li><li><p>Scoring counts the track as entering volume |
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| 119 | <span class="emphasis"><em>A</em></span></p></li></ol></div></li><li><p>Step:</p><p>The step may be limited by any process.</p><p>Transportation locates particle at the new |
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| 120 | position </p></li></ol></div></dd><dt><span class="term"><span class="emphasis"><em>Comment:</em></span></span></dt><dd><p>See the comment in <a href="#mass-parent-ms" title="2.1. Particle suffers multiple scattering">Section 2.1</a>.</p></dd></dl></div></div><div class="sect1"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="parallel-parent-zero"></a>3.2. Particle suffers physics process on boundary</h2></div></div><div class="variablelist"><dl><dt><span class="term"><span class="emphasis"><em>Description:</em></span></span></dt><dd><p>A particle step is limited by a boundary in the parallel |
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| 121 | geometry between volumes <span class="emphasis"><em>A</em></span> and |
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| 122 | <span class="emphasis"><em>B</em></span>. A physics process returns |
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| 123 | step length = 0.</p></dd><dt><span class="term"><span class="emphasis"><em>Relevance:</em></span></span></dt><dd><p> |
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| 124 | See <a href="#mass-parent-zero" title="2.2. Parent particle suffers process on mass-boundary">Section 2.2</a>. |
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| 125 | </p></dd><dt><span class="term"><span class="emphasis"><em>Figure:</em></span></span></dt><dd><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0"><tr><td><img src="figures/parallel-parent-zero.gif" alt="Particle suffers process on boundary."></td></tr></table><div class="caption"><p>A parent particle crosses the boundary in the parallel |
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| 126 | geometry. A physics process happens on the boundary.</p></div></div></dd><dt><span class="term"><span class="emphasis"><em>Detailed description:</em></span></span></dt><dd><p>Three steps <span class="emphasis"><em>1</em></span>, <span class="emphasis"><em>2</em></span>, |
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| 127 | <span class="emphasis"><em>3</em></span> occur:</p><div class="orderedlist"><ol type="1"><li><p><a name="parallel-parent-zero-step-1"></a>Step:</p><div class="orderedlist"><ol type="a"><li><p>The step is limited by a boundary in the parallel |
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| 128 | geometry found by the ParallelImportanceProcess.</p></li><li><p>Transportation moves the particle in the mass |
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| 129 | geometry.</p></li><li><p>The ParallelImportanceProcess |
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| 130 | moves the particle on the boundary and locates it |
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| 131 | in volume <span class="emphasis"><em>B</em></span> of the parallel geometry. |
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| 132 | Biasing splits or plays Russian Roulette and changes the weight.</p><p>The ParallelImportanceProcess may create daughters |
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| 133 | see <a href="#parallel-bias-daughter" title="3.4. Daughter created by biasing">Section 3.4</a></p></li><li><p>Scoring counts a track entering.</p></li></ol></div></li><li><p>Step:</p><div class="orderedlist"><ol type="a"><li><p>A physics process retruns step length = 0.</p></li><li><p>Scoring counts a collision in volume |
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| 134 | <span class="emphasis"><em>B</em></span></p></li><li><p>The physics process changes the momentum |
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| 135 | of the particle and creates a daughter |
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| 136 | (See <a href="#parallel-phys-daughter" title="3.3. Daughter created by a physics process on a boundary">Section 3.3</a>). Both momentums point |
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| 137 | towards volume <span class="emphasis"><em>A</em></span>.</p></li></ol></div></li><li><p>Step:</p><div class="orderedlist"><ol type="a"><li><p>The ParallelImportanceProcess limits the |
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| 138 | step.</p></li><li><p>The ParallelImportanceProcess locates it |
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| 139 | in volume <span class="emphasis"><em>A</em></span> of the parallel geometry. |
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| 140 | Biasing splits or plays Russian Roulette and changes the weight.</p><p>The ParallelImportanceProcess may create daughters |
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| 141 | see <a href="#parallel-bias-daughter" title="3.4. Daughter created by biasing">Section 3.4</a></p></li><li><p>Scoring counts a track entering volume |
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| 142 | <span class="emphasis"><em>A</em></span>.</p></li></ol></div></li></ol></div></dd><dt><span class="term"><span class="emphasis"><em>Comment:</em></span></span></dt><dd><p> |
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| 143 | This way should be correct. |
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| 144 | </p></dd></dl></div></div><div class="sect1"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="parallel-phys-daughter"></a>3.3. Daughter created by a physics process on a boundary</h2></div></div><div class="variablelist"><dl><dt><span class="term"><span class="emphasis"><em>Description:</em></span></span></dt><dd><p> |
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| 145 | A particle step reaches a boundary in the parallel geometry between volume |
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| 146 | <span class="emphasis"><em>A</em></span> and volume <span class="emphasis"><em>B</em></span>. A physical |
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| 147 | process returns steplength =0 and creates a daughter.</p></dd><dt><span class="term"><span class="emphasis"><em>Relevance:</em></span></span></dt><dd><p> |
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| 148 | See <a href="#mass-phys-daughter" title="2.3. Daughter created by a physics process on boundary">Section 2.3</a>. |
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| 149 | </p></dd><dt><span class="term"><span class="emphasis"><em>Figure:</em></span></span></dt><dd><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0"><tr><td><img src="figures/parallel-phys-daughter-zero.gif" alt="A process creates a daughter on the boundary."></td></tr></table><div class="caption"><p>A process creates a daughter on the boundary.</p></div></div></dd><dt><span class="term"><span class="emphasis"><em>Detailed description:</em></span></span></dt><dd><p>The description of |
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| 150 | two steps of the particle and the first step of |
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| 151 | the daughter created by a physical process on the boundary:</p><div class="orderedlist"><ol type="1"><li><p><span class="emphasis"><em>Cross boundary.</em></span></p><p>This is equivalent to step one in |
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| 152 | <a href="#parallel-parent-zero" title="3.2. Particle suffers physics process on boundary">Section 3.2</a></p></li><li><p><span class="emphasis"><em>Physics process.</em></span></p><div class="orderedlist"><ol type="a"><li><p>A physics process returns step length = 0.</p></li><li><p>Scoring may count collsision with the original |
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| 153 | track momentum and the correct weight.</p></li><li><p>The physics process changes the momentum of the |
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| 154 | particle and creates a daughter with momentum pointing to |
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| 155 | volume <span class="emphasis"><em>A</em></span>.</p></li></ol></div></li><li><p> |
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| 156 | First step <span class="emphasis"><em>1.d</em></span> of daughter</p><p><span class="strong"><em>According to the |
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| 157 | momentum the daughter is located in |
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| 158 | volume</em></span> <span class="emphasis"><em>A</em></span> <span class="strong"><em>. |
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| 159 | </em></span></p><p>The ParallelImportanceProcess <span class="emphasis"><em>does not |
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| 160 | </em></span> occur. Therefore no biasing is applied and the |
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| 161 | weight is not changed!</p></li><li><p>Scoring counts a collision in volume |
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| 162 | <span class="emphasis"><em>A</em></span> <span class="emphasis"><em>with the wrong weight</em></span>. |
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| 163 | </p></li></ol></div></dd><dt><span class="term"><span class="emphasis"><em>Comment:</em></span></span></dt><dd><p> |
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| 164 | Locating the daughter particle in volume <span class="emphasis"><em>A</em></span> |
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| 165 | is wrong. |
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| 166 | </p></dd></dl></div></div><div class="sect1"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="parallel-bias-daughter"></a>3.4. Daughter created by biasing</h2></div></div><div class="variablelist"><dl><dt><span class="term"><span class="emphasis"><em>Description:</em></span></span></dt><dd><p> |
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| 167 | A parent particle crosses the boundary in the parallel |
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| 168 | geometry. Biasing creates copies of the particle. |
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| 169 | </p></dd><dt><span class="term"><span class="emphasis"><em>Relevance:</em></span></span></dt><dd><p> |
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| 170 | See <a href="#mass-bias-daughter" title="2.4. Daughter created by biasing">Section 2.4</a>. |
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| 171 | </p></dd><dt><span class="term"><span class="emphasis"><em>Figure:</em></span></span></dt><dd><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" cellspacing="0" cellpadding="0"><tr><td><img src="figures/parallel-bias-daughter.gif" alt="A daughter created by biasing"></td></tr></table><div class="caption"><p>A particle crosses the boundary in the parallel |
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| 172 | geometry. Biasing creates copies.</p></div></div></dd><dt><span class="term"><span class="emphasis"><em>Detailed description:</em></span></span></dt><dd><p> |
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| 173 | A step <span class="emphasis"><em>1</em></span> of the parent and the |
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| 174 | first step <span class="emphasis"><em>1.d</em></span> are shown:</p><div class="orderedlist"><ol type="1"><li><p><span class="emphasis"><em>Step</em></span></p><div class="orderedlist"><ol type="a"><li><p>Step one is limited by a boundary in |
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| 175 | the parallel geometry found by ParallelImportanceProcess. The |
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| 176 | ParallelImportanceProcess moves the particle on the boundary and |
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| 177 | locates it in volume <span class="emphasis"><em>B</em></span>.</p></li><li><p>Biasing split's or deletes the particle |
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| 178 | and changes weight correctly.</p></li><li><p>Scoring counts the track as entering volume |
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| 179 | <span class="emphasis"><em>B</em></span></p></li></ol></div></li><li><p><span class="emphasis"><em>1.d: first step of daughter</em></span></p><div class="orderedlist"><ol type="a"><li><p>The ParallelImportanceProcess locates the daughter |
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| 180 | in <span class="emphasis"><em>B</em></span>.</p></li><li><p>Any process may limit the step.</p></li></ol></div></li></ol></div></dd><dt><span class="term"><span class="emphasis"><em>Comment:</em></span></span></dt><dd><p> |
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| 181 | This should be the correct way. |
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| 182 | </p></dd></dl></div></div></div><div class="chapter"><div class="titlepage"><div><h2 class="title"><a name="problems"></a>Chapter 4. To the problematic usecases</h2></div></div><p>Of this (probably incomplete) list of usecases the cases |
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| 183 | <a href="#mass-parent-ms" title="2.1. Particle suffers multiple scattering">Section 2.1</a>, |
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| 184 | <a href="#parallel-parent" title="3.1. Particle suffers multiple scattering.">Section 3.1</a> and |
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| 185 | <a href="#parallel-phys-daughter" title="3.3. Daughter created by a physics process on a boundary">Section 3.3</a> are treated wrongly. |
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| 186 | The first two cases apply to charged particles only. The other |
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| 187 | usecase applies for the parallel geometry. Therefore this documents |
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| 188 | does not contain problematic usecases for neutral particles in the mass |
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| 189 | geometry. </p><p>The only wrongly treated usecase in this document |
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| 190 | applying also for neutral particles is |
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| 191 | <a href="#parallel-phys-daughter" title="3.3. Daughter created by a physics process on a boundary">Section 3.3</a>. </p><p>The reason for the problem is: In contrast to the mass |
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| 192 | geometry cases there is no information about the current Touchable in |
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| 193 | the parallel geometry related to a newly starting particle.</p><p>The two types of particles starting on a parallel boundary |
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| 194 | are:</p><div class="orderedlist"><ol type="1"><li><p> <a href="#parallel-phys-daughter" title="3.3. Daughter created by a physics process on a boundary">Section 3.3</a> particles |
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| 195 | created by a physical process on the boundary.</p></li><li><p><a href="#parallel-bias-daughter" title="3.4. Daughter created by biasing">Section 3.4</a> particles created |
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| 196 | by importance sampling. All particles created by importance |
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| 197 | sampling start on a boundary.</p></li></ol></div><p>The particles starting on the boundary may be located |
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| 198 | in either of both volumes depending on the geometry |
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| 199 | e.g. which volume is deepest.</p><p>In order to treat the much more frequent cases of type |
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| 200 | number 2. correct it has been chosen to take the direction of the |
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| 201 | particle momentum into account. But this treats the cases of |
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| 202 | type 1. wrong.</p><p>To solve this problem it has been considered to somehow |
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| 203 | provide the information about the Touchable in the parallel geometry. |
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| 204 | It is not clear "who" should give that information to "whom". |
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| 205 | While the importance sampling process knows about the parallel |
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| 206 | geometry and therefore could assign a touchable to the particle |
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| 207 | in principle, the physics processes can't do that.</p></div><div class="chapter"><div class="titlepage"><div><h2 class="title"><a name="summary"></a>Chapter 5. Summary</h2></div></div><p>This document gives a list of usecases which should be |
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| 208 | considered for the implementation of importance sampling and |
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| 209 | scoring. </p><p>When changing the behaviour of importance sampling |
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| 210 | the resulting algorithm should be checked at least against the |
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| 211 | usecases listed here.</p><p>The current problem to be solved is to treat |
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| 212 | the usecase <a href="#parallel-phys-daughter" title="3.3. Daughter created by a physics process on a boundary">Section 3.3</a> right |
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| 213 | without messing up usecase <a href="#parallel-bias-daughter" title="3.4. Daughter created by biasing">Section 3.4</a> |
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| 214 | .</p></div></div></body></html> |
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