| Previous Topic | Next Topic | Contents | Features |
The union of bodies A and B, denoted by A : B, is that space that is inside body A, body B, or within both. The bodies on either side of the union operator may carry an explicit sign. A union will not necessarily add back excluded volume: A -C -B :B is not the same as A -C. A zone description that contains a union is known as a complex zone.
In the hierarchy of Boolean operators for body geometry, the union operator is the highest, regardless of parentheses. Consider a case where 2 intersecting spheres, bodies 1 and 2, are contained within body 10, a larger sphere:
sphere 1 3 0 0 5
sphere 2 0 3 0 5
sphere 10 0 0 0 10
The intersection of the smaller spheres is 1 2. The remainder of the volume enclosed by the larger sphere, i.e., within body 10 but not in the intersection of 1 and 2, cannot be defined as the intersection of inside 10 with the union of space not in 1 and not in 2, as in
10 (-1 : -2 )
Because of the operator precedence, this volume is the union of space within 10 and not in 1 with space within 10 and not in 2:
10 -1 : 10 -2
The union operator in body geometry description is not the same as the union operator in MCNP cell descriptions.
By use of the union operator, several disjointed volumes may be combined into a single zone. The individual connected elements of such a disconnected volume, known as code zones, are the logical entities handled internally by Sabrina. The combination of several code zones into a single input zone is provided for convenience of user input. Complex zone descriptions are a hindrance to efficient rendering and, in MCNP, tracking, and should be avoided in favor of simple zones if possible.