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documentation/lagrit_manual/commands/region.txt

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+.. _region :
+
+&nbsp_place_holder;
+
+> **_REGION_**
+
+>
+
+>> Define a geometric region from the set of surfaces by logically combining
+the surface names.&nbsp_place_holder; A region may be removed from the
+geometry by specifying the release keyword.
+
+>>
+
+>> To define a region, the operators **lt, le, gt, and ge** are applied to
+previously defined surfaces according to the following rules.
+
+>>
+
+>>> **lt** -- if the surface following is a volume then lt means inside not
+including the surface of the volume. If the surface is a plane or a sheet lt
+means the space on the side of the plane or sheet opposite to the normal not
+including the plane or sheet itself.
+
+**le** -- if the surface following is a volume then le means inside including the surface of the volume. If the surface is a plane or a sheet le means the space on the side of the plane or sheet opposite to the normal including the plane or sheet itself.   
+**gt** -- if the surface following is a volume then gt means outside not including the surface of the volume. If the surface is a plane or a sheet **gt** means the space on the same side of the plane or sheet as the normal not including the plane or sheet itself.   
+**ge** -- if the surface following is a volume then ge means outside including the surface of the volume. If the surface is a plane or a sheet **ge** means the space on the same side of the plane or sheet as the normal including the plane or sheet itself.   
+The operators or, and, and not applied to surfaces mean union, intersection
+and complement respectively. The parentheses operators, (and ), are used for
+nesting. Spaces are required as delimiters to separate all operators and
+operands. Internal interfaces should be included in exactly one region. In the
+event of conflicting region commands, the one occurring last in the input
+stream takes precedence.
+
+>>>
+
+>>> Defining a&nbsp_place_holder; region will cause the information associated
+with this material region to be stored under the name of the [geometry
+](../geometries.html)of the current mesh object.&nbsp_place_holder; Releasing
+the&nbsp_place_holder; region will remove this information.
+
+>
+
+> FORMAT:
+
+>
+
+>> **region/**region_name/region definition
+
+**region/**region_name/**release**   
+&nbsp_place_holder;
+
+>
+
+> EXAMPLES:
+
+>
+
+>> **region**/reg1/**le** sphere1 **and** ( **lt** plane1 **or** **gt** plane2
+)
+
+**region**/reg2/**le** sphere1 **and** ( **ge** plane1 **and** **le** plane2 )   
+**region**/reg1/**release**   
+&nbsp_place_holder;
+