gsignal: Graph Object with a Signal

Description

This function constructs an igraph graph object with several vertex and edge attributes.

Usage

gsignal(vertex, edge, edgetype = c("matrix", "list"))

Value

an igraph graph object. The vertex attributes are vertex coordinate x, y, and a signal z on each vertex. The edge attribute is weight. These vertex and edge attributes can be identified by names(vertex_attr()) and names(edge_attr()), and are accessible by V(), E(), as_edgelist(), as_adjacency_matrix() or other igraph functions.

Arguments

vertex: matrix or data.frame containing vertex information. The first two columns are vertex coordinate x, y, and the third column is a signal z on each vertex.
edge: When edgetype="matrix", a square weighted adjacency matrix. This can be a sparse matrix created with Matrix package. When edgetype="list", matrix or data.frame of edge list with three columns. The first two columns are edge lists and the third column is an edge weight.
edgetype: edges and weights information are provided by "matrix" or "list".

Details

This function constructs an igraph graph object with vertex and edge attributes.

Examples

Run this code

#### example : composite of two components having different frequencies

## define vertex coordinate
x <- y <- seq(0, 1, length=30)
xy <- expand.grid(x=x, y=y)

## weighted adjacency matrix by Gaussian kernel 
## for connecting vertices within distance 0.04
A <- adjmatrix(xy, method = "dist", 0.04) 

## signal
# high-frequency component
signal1 <- rep(sin(12.5*pi*x - 1.25*pi), 30)

# low-frequency component
signal2 <- rep(sin(5*pi*x - 0.5*pi), 30)

# composite signal
signal0 <- signal1 + signal2

# noisy signal with SNR(signal-to-noise ratio)=5
signal <- signal0 + rnorm(900, 0, sqrt(var(signal0) / 5)) 

# graph with signal
gsig <- gsignal(vertex = cbind(xy, signal), edge = A, edgetype = "matrix")

# vertex and edge attribute
names(vertex_attr(gsig)); names(edge_attr(gsig))

# edge list
# as_edgelist(gsig, name=FALSE)

# weighted adjacency matrix
# as_adjacency_matrix(gsig, attr="weight")

# display a noisy graph signal 
gplot(gsig, size=3)

# display a composite graph signal 
gplot(gsig, signal0, size=3)

# display high-frequency component
gplot(gsig, signal1, size=3)

# display low-frequency component
gplot(gsig, signal2, size=3)