| 1 | <head> |
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| 2 | <title>Element Classes</title> |
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| 3 | <!-- Changed by: Chris ISELIN, 24-Jan-1997 --> |
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| 4 | <!-- Changed by: Hans Grote, 25-Sep-2002 --> |
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| 5 | </head> |
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| 6 | |
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| 7 | <body bgcolor="#ffffff"> |
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| 8 | |
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| 9 | <h1>Element Classes</h1> |
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| 10 | |
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| 11 | The concept of element classes solves the problem of addressing |
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| 12 | instances of elements in the accelerator in a convenient manner. |
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| 13 | It will first be explained by an example. |
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| 14 | All the quadrupoles in the accelerator form a class QUADRUPOLE. |
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| 15 | Let us define three subclasses for the focussing quadrupoles, |
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| 16 | the defocussing quadrupoles, and the skewed quadrupoles: |
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| 17 | <pre> |
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| 18 | MQF: QUADRUPOLE,L=LQM,K1=KQD; ! Focussing quadrupoles |
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| 19 | MQD: QUADRUPOLE,L=LQM,K1=KQF; ! Defocussing quadrupoles |
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| 20 | MQT: QUADRUPOLE,L=LQT; ! Skewed quadrupoles |
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| 21 | </pre> |
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| 22 | These classes can be thought of as new keywords which define |
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| 23 | elements with specified default attributes. |
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| 24 | We now use theses classes to define the real quadrupoles: |
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| 25 | <pre> |
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| 26 | QD1: MQD; ! Defocussing quadrupoles |
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| 27 | QD2: MQD; |
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| 28 | QD3: MQD; |
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| 29 | ... |
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| 30 | QF1: MQF; ! Focussing quadrupoles |
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| 31 | QF2: MQF; |
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| 32 | QF3: MQF; |
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| 33 | ... |
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| 34 | QT1: MQT,K1S=KQT1; ! Skewed quadrupoles |
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| 35 | QT2: MQT,K1S=KQT2; |
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| 36 | ... |
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| 37 | </pre> |
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| 38 | These quadrupoles inherit all unspecified attributes from their class. |
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| 39 | This allows to build up a hierarchy of objects with a rather |
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| 40 | economic input structure. |
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| 41 | <p> |
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| 42 | The full power of the class concept is revealed when object classes |
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| 43 | are used to select instances of elements for various purposes. |
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| 44 | Example: |
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| 45 | <pre> |
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| 46 | select,flag=twiss,class=QUADRUPOLE; ! Select all quadrupoles for the |
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| 47 | ! Twiss TFS file |
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| 48 | </pre> |
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| 49 | <p> |
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| 50 | More formally, for each element keyword MAD maintains a |
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| 51 | class of elements with the same name. |
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| 52 | A defined element becomes itself a class which can be used |
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| 53 | to define new objects, |
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| 54 | which will become members of this class. |
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| 55 | A new object inherits all attributes from its class; |
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| 56 | but its definition may override some of those values by new ones. |
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| 57 | All class and object names can be used in range selections, |
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| 58 | providing a powerful mechanism to specify positions |
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| 59 | for matching constraints and printing. |
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| 60 | |
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| 61 | <address><a href="http://www.cern.ch/Hans.Grote/hansg_sign.html">hansg</a>, |
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| 62 | January 24, 1997 |
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| 63 | </address> |
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| 64 | |
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| 65 | </body> |
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