[NeXus-definitions-tickets] [NeXusDefinitions] #32: dimensions in NXDL

[NeXus Base Classes and Instrument Definitions]

#32: dimensions in NXDL
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Reporter:  Pete Jemian  |       Owner:  Pete Jemian     
    Type:  task         |      Status:  assigned        
Priority:  major        |   Milestone:  release NXDL 1.0
Keywords:               |  
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Comment(by Pete Jemian):

 now, back to the present...

 {{{
 On 11/27/2010 12:13 PM, Pete R Jemian wrote:
 >
 > For array indices, there is an example in NXcrystal that defines array
 dimensions:

     <field name="unit_cell" type="NX_FLOAT" units="NX_LENGTH">
         <doc>Unit cell parameters (lengths and angles)</doc>
         <dimensions rank="2"><!--[n_comp,6]-->
             <dim index="1" value="n_comp"/>
             <dim index="2" value="6"/>
         </dimensions>
     </field>

 >
 > This definition implies there are "n_comp" different sets (first index)
 > of unit cell parameters (3 lengths and 3 angles as the second index).
 >
 > There is other complexity possible in the "dim" element using the "ref"
 > and "refindex" attributes.  Also, the "value" attribute can be an
 > algebraic expression such as "n + 2".  See the manual for the
 > information that is available:
 > http://download.nexusformat.org/doc/html/bk02ch02s02.html#id1354248
 > (Note that the manual still needs some work here since the "rank"
 > attribute belongs with the "dimensions" element while the other
 > attributes shown go with the "dim" element.  I'll work on that soon.)


 I propose to add a bit more structure at the top of an
 NXDL specification that will define each of the algebraic
 variables used to describe the length of a dimension.
 This would be useful for validation of a data file against
 an NXDL and for a person to better understand the intent
 as it is used in an NXDL file.  An example for this
 NXcrystal instance would be:

     <NXDL_symbols>
         <symbol name="n_comp">
             <doc>number different unit cells to be described</doc>
         </symbol>
     </NXDL_symbols>
 }}}

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Ticket URL: <http://trac.nexusformat.org/definitions/ticket/32#comment:12>
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