.. _mregion :

&nbsp_place_holder;

> **_MREGION_**

>

>> Define a material region from a set of surfaces by logically combining the
surface names and region names. A material region may be removed from the
geometry by specifying the release keyword.

>>

>> To define material rgion, the operator **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 regions or modified surfaces mean union, intersection and complement respectively. Parentheses are operators and are used for nesting. Spaces are required as delimiters to separate operators and operands; parentheses are operators and must be surrounded by spaces. Internal interfaces should be excluded when defining material regions. (i.e. use **lt** and **gt** ). External boundaries should be included when defining material regions. If a material regions consists of more than one region and the regions touch (i.e. share a region interface), then the region interface is not a material interface -- all the points on the region interface are interior to the material region. In this case use **le **or** ge** to include these region interface points in the material region as interior points. 

Defining a material 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 material region will remove this information.

&nbsp_place_holder; FORMAT:
&nbsp_place_holder;**mregion/**material_region_name/region definition
EXAMPLES: **mregion/ **material_region_name/**release**

**mregion**/mat1/** le **box1 **and **(** lt** sphere1 **and** ( **lt** plane1 **or gt** plane2 ) ) /   
**mregion**/mat2/ regiona **or** regionb /