Physical Groups and Periodicity¶

Physical groups give application meaning to geometric entities and elements. Periodic links describe slave-to-master entity and node relationships. Both are available from the modern model returned by gmshparser.read().

Physical groups¶

Named groups from $PhysicalNames and assignments from supported MSH sections are collected in mesh.physical_groups.

import gmshparser

mesh = gmshparser.read("mesh.msh")

walls = mesh.physical_groups["Walls"]
domain = mesh.physical_groups[(3, 2)]

A name lookup is valid only when the name is unique. Use (dimension, tag) when the same name appears in more than one dimension.

print(walls.dimension)
print(walls.tag)
print(walls.name)
print(walls.entities)
print(walls.elements)
print(walls.nodes)

The convenience method accepts a name or numeric tag:

walls = mesh.physical_group("Walls")
domain = mesh.physical_group(2, dimension=3)

A numeric tag without dimension= is accepted only when it identifies one group unambiguously.

Filter by physical tag¶

Physical assignments are also available directly on nodes, elements, and entities.

wall_elements = mesh.elements.where(physical_tag=10)
wall_nodes = mesh.nodes.where(physical_tag=10)
wall_entities = mesh.entities.where(physical_tag=10)

Use mesh.physical_groups when you need the resolved group object and its name. Use collection filters when the tag is already known and you only need selected mesh values.

Anonymous groups¶

MSH 1.0 and files without $PhysicalNames may contain physical assignments without names. These groups remain accessible by (dimension, tag):

boundary = mesh.physical_groups[(2, 10)]
assert boundary.name is None

Periodic links¶

Supported MSH 2.x and 4.x $Periodic sections are exposed through mesh.periodic_links.

link = mesh.periodic_links[(2, 7)]

print(link.dimension)
print(link.entity_tag)
print(link.master_entity_tag)
print(link.affine_transform)
print(link.node_pairs)

Each node pair is (slave_node_tag, master_node_tag) in file order:

for slave_tag, master_tag in link.node_pairs:
    slave = mesh.nodes[slave_tag]
    master = mesh.nodes[master_tag]
    print(slave.coordinates, master.coordinates)

Filter periodic relations by dimension:

surface_links = mesh.periodic_links.by_dimension(2)

The convenience method avoids constructing a tuple key:

link = mesh.periodic_link(dimension=2, tag=7)

Compatibility API¶

The original mutable model exposes periodic data through get_periodic_link() and get_periodic_links(). Physical names and assignments are also retained, but new code should prefer the resolved modern collections.

See Modern Data Model for collection behavior and Supported Formats for version-specific retention rules.