nearest
Nearest neighbors within radius
Description
uses additional options specified by one or more name-value pair arguments. For
example, if nodeIDs
= nearest(G
,s
,d
,Name,Value
)G
is a weighted graph, then
nearest(G,s,d,'Method','unweighted')
ignores the edge weights
in graph G
and instead treats all edge weights as
1
.
Examples
Nearest Nodes
Create and plot a graph with weighted edges.
s = [1 1 1 1 1 2 2 2 3 3 3 3 3]; t = [2 4 5 6 7 3 8 9 10 11 12 13 14]; weights = randi([1 10],1,13); G = graph(s,t,weights); p = plot(G,'Layout','force','EdgeLabel',G.Edges.Weight);
Determine which nodes are within a radius of 15 from node 1.
nn = nearest(G,1,15)
nn = 9×1
5
7
2
3
4
6
8
12
9
Highlight the source node as green and the nearest neighbors as red.
highlight(p,1,'NodeColor','g') highlight(p,nn,'NodeColor','r')
Distances of Nearest Nodes
Create and plot a graph with weighted edges.
s = [1 1 1 2 2 6 6 7 7 3 3 9 9 4 4 11 11 8];
t = [2 3 4 5 6 7 8 5 8 9 10 5 10 11 12 10 12 12];
weights = [10 10 10 10 10 1 1 1 1 1 1 1 1 1 1 1 1 1];
G = graph(s,t,weights);
plot(G,'EdgeLabel',G.Edges.Weight)
Determine which nodes are within a radius of 5 from node 3, and return the distance to each node.
[nn,dist] = nearest(G,3,5)
nn = 9×1
9
10
5
11
4
7
12
6
8
dist = 9×1
1
1
2
2
3
3
3
4
4
Incoming Neighbor Distances in Directed Graph
Create and plot a directed graph with weighted edges.
s = {'a' 'a' 'a' 'b' 'c' 'c' 'e' 'f' 'f'}; t = {'b' 'c' 'd' 'a' 'a' 'd' 'f' 'a' 'b'}; weights = [1 1 1 2 2 2 2 2 2]; G = digraph(s,t,weights); plot(G,'EdgeLabel',G.Edges.Weight)
Determine the nearest nodes within a radius of 1 from node 'a'
, measured by outgoing path distance from node 'a'
.
nn_out = nearest(G,'a',1)
nn_out = 3x1 cell
{'b'}
{'c'}
{'d'}
Determine all of the nodes that have incoming paths leading to node 'a'
by specifying the radius as Inf
.
nn_in = nearest(G,'a',Inf,'Direction','incoming')
nn_in = 4x1 cell
{'b'}
{'c'}
{'f'}
{'e'}
Input Arguments
s
— Source node
node index | node name
Source node, specified as a node index or a node name in one of the forms in this table.
Value | Example |
---|---|
Scalar node index | 1 |
Character vector node name | 'A' |
String scalar node name | "A" |
Example: nearest(G,3,1)
Example: nearest(G,'a',5)
d
— Neighbor distance radius
scalar
Neighbor distance radius, specified as a numeric scalar.
Example: nearest(G,3,1)
Example: nearest(G,'a',2.5)
Name-Value Arguments
Specify optional pairs of arguments as
Name1=Value1,...,NameN=ValueN
, where Name
is
the argument name and Value
is the corresponding value.
Name-value arguments must appear after other arguments, but the order of the
pairs does not matter.
Before R2021a, use commas to separate each name and value, and enclose
Name
in quotes.
Example: [nodeIDs,dist] =
nearest(G,s,5,'Method','unweighted','Direction','incoming')
Direction
— Direction of distance measurement
'outgoing'
(default) | 'incoming'
Note
The 'Direction'
option can only be specified
with directed graphs.
Direction of distance measurement, specified as the comma-separated
pair consisting of 'Direction'
and one of the options
in this table.
Option | Description |
---|---|
'outgoing' (default) | Distances are calculated using paths going
out from source node
s . |
'incoming' | Distances are calculated using paths coming
in to source node
s . |
Example: nearest(G,s,d,'Direction','incoming')
Method
— Shortest path algorithm
'auto'
(default) | 'unweighted'
| 'positive'
| 'mixed'
Shortest path algorithm, specified as the comma-separated pair
consisting of 'Method'
and one of the options in this
table.
Option | Description |
---|---|
'auto' (default) |
The
|
'unweighted' |
Breadth-first computation that treats all edge
weights as |
'positive' |
Dijkstra algorithm that requires all edge weights to be nonnegative. |
'mixed' (only for
digraph ) |
Bellman-Ford algorithm for directed graphs that requires the graph to have no negative cycles. While |
Note
For most graphs, 'unweighted'
is the fastest
algorithm, followed by 'positive'
and
'mixed'
.
Example: nearest(G,s,d,'Method','positive')
Output Arguments
nodeIDs
— Nearest neighbor node IDs
node indices | node names
Nearest neighbor node IDs, returned as node indices if
s
is numeric, or as node names if
s
is a node name. The nodes are sorted from nearest
to furthest. nodeIDs
is empty if no nodes are within the
specified distance. nodeIDs
never contains the source
node s
even if the graph has self-loops.
Use H = subgraph(G,[s; nodeIDs])
to extract a subgraph
of the nearest neighbors from the original graph
G
.
dist
— Neighbor distances
vector
Neighbor distances, returned as a vector. dist(j)
is
the distance from source node s
to neighboring node
nodeIDs(j)
.
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.
Name value arguments must be constant.
Only the
'positive'
,'unweighted'
and'auto'
methods are supported.
Thread-Based Environment
Run code in the background using MATLAB® backgroundPool
or accelerate code with Parallel Computing Toolbox™ ThreadPool
.
Version History
Introduced in R2016a
See Also
shortestpath
| distances
| shortestpathtree
| neighbors
| successors
| predecessors
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