# Source code for landlab.graph.hex.dual_hex

```import numpy as np

from ..dual import DualGraph
from ..voronoi.dual_voronoi import DualVoronoiGraph
from .hex import (
HorizontalHexTriGraph,
HorizontalRectTriGraph,
TriGraph,
VerticalHexTriGraph,
VerticalRectTriGraph,
)

[docs]class DualHexGraph(DualGraph, TriGraph):

"""Graph of a structured grid of triangles.

Examples
--------
>>> import numpy as np
>>> from landlab.graph import DualHexGraph

>>> graph = DualHexGraph((3, 2), node_layout='hex')
>>> graph.number_of_nodes
7
>>> graph.number_of_corners
6

>>> np.round(graph.y_of_node * 2. / np.sqrt(3))
...     # doctest: +NORMALIZE_WHITESPACE
array([ 0.,  0.,  1.,  1.,  1.,  2.,  2.])
>>> graph.x_of_node # doctest: +NORMALIZE_WHITESPACE
array([ 0.5,  1.5,  0. ,  1. ,  2. ,  0.5,  1.5])
"""

[docs]    def __init__(
self,
shape,
spacing=1.0,
xy_of_lower_left=(0.0, 0.0),
orientation="horizontal",
node_layout="rect",
sort=False,
):
"""Create a structured grid of triangles.

Parameters
----------
shape : tuple of int
Number of rows and columns of the hex grid. The first value
is the number of nodes in the first column and the second the
number of nodes in the first column.
spacing : float, optional
xy_of_lower_left : tuple of float, optional
Coordinates of lower-left corner of the grid.
orientation: {'horizontal', 'vertical'}
Specify if triangles should be laid out in rows or columns.
node_layout: {'rect', 'hex'}
Specify the overall layout of the nodes. Use *rect* for
the layout to approximate a rectangle and *hex* for
a hexagon.
"""
if node_layout not in ("rect", "hex"):
raise ValueError("node_layout not understood")

if orientation not in ("horizontal", "vertical"):
raise ValueError("orientation not understood")

layouts = {
"horizontal_hex": HorizontalHexTriGraph,
"vertical_hex": VerticalHexTriGraph,
"horizontal_rect": HorizontalRectTriGraph,
"vertical_rect": VerticalRectTriGraph,
}
layout = layouts["_".join([orientation, node_layout])]

try:
spacing = float(spacing)
except TypeError as exc:
raise TypeError("spacing must be a float") from exc

self._shape = tuple(shape)
self._spacing = spacing
self._orientation = orientation
self._node_layout = node_layout

x_of_node, y_of_node = layout.xy_of_node(
shape, spacing=spacing, xy_of_lower_left=xy_of_lower_left
)
self._perimeter_nodes = layout.perimeter_nodes(shape)