= How to create your GEAR XML steering file =
This post is a small guide on how to create your own GEAR file with GEAR v0.12, the first with multi-module capabilities. I will include a code example for each section of the description.

A more extensive guide by Martin Killenberg can be found at https://agenda.linearcollider.org/event/5902/contribution/2/2/material/0/0.pdf It gives special attention to gear files for the Large Prototype TPC.

The root element of any GEAR XML steering file is gear

== Children of gear ==
The only element that are currently looked for in the first layer of the tree structure of the XML file are:

 * global which can only contain the attribute detectorName which is a string that defines, guess what, the detector name.
 * BField which define the magnetic field in the detector and contaon 4 attributes
  . o type is a string which defines what implementation to use to create a megnetic field object. As of August 2009 the only value available for this field is ConstantBField
  . o x defines the x component of the B vector (double)
  . o y defines the y component of the B vector (double)
  . o z defines the z component of the B vector (double)
 * detectors which contain a list of detector elements that will be described later

The first example of the first layer of the XML tree is:

{{{
<gear>

 . <global detectorName="!MyExperiment" />
 . <BField type="ConstantBField" x="0." y="0." z="4.0" /> <detectors>
  . [Put your detector list here]
 </detectors>

</gear>
}}}
== Defining your detector ==
The only type of element that can be defined has child of a detectors element is a detector (notice the lack of s). Infact the detectors element is but a list of detector items.

Each detector has two mandatory attributes which:

 * name which is a custom identifier for the particular detector
 * geartype which defines the specific type of the detector. This parameter is a string that must correspond to one of the gear detector types. For the TPC this is TPCParameters

The elements that can be contained in a detector are detector-specific. In the following I will describe the parameters necessary to describe a TPC.

Let's now fill the example a little more:

{{{
<gear>

 . <global detectorName="!MyExperiment" />
 . <BField type="ConstantBField" x="0." y="0." z="4.0" /> <detectors>
  . <detector name="MyTPC" geartype="TPCParameters">
  .      [Define your TPC here]
  . </detector>
 </detectors>

</gear>
}}}
[TO BE CONTINUED]

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comment: original post by Stefano Caiazza (copied here by C.R.)