riem.clrq: Competitive Learning Riemannian Quantization

In Riemann: Learning with Data on Riemannian Manifolds

Competitive Learning Riemannian Quantization

Description

Given N observations X_1, X_2, …, X_N \in \mathcal{M}, perform clustering via Competitive Learning Riemannian Quantization (CLRQ). Originally, the algorithm is designed for finding voronoi cells that are used in domain quantization. Given the discrete measure of data, centers of the cells play a role of cluster centers and data are labeled accordingly based on the distance to voronoi centers. For an iterative update of centers, gradient descent algorithm adapted for the Riemannian manifold setting is used with the gain factor sequence

γ_t = \frac{a}{1 + b √{t}}

where two parameters a,b are represented by par.a and par.b. For initialization, we provide k-means++ and random seeding options as in k-means.

Usage

riem.clrq(riemobj, k = 2, init = c("plus", "random"), gain.a = 1, gain.b = 1)

Arguments

riemobj	a S3 "riemdata" class for N manifold-valued data.
k	the number of clusters.
init	(case-insensitive) name of an initialization scheme. (default: "plus".)
gain.a	parameter a for gain factor sequence.
gain.b	parameter b for gain factor sequence.

Value

a named list containing

centers

a 3d array where each slice along 3rd dimension is a matrix representation of class centers.

cluster

a length-N vector of class labels (from 1:k).

References

\insertRef

lebrigant_quantization_2019Riemann

\insertRef

bonnabel_stochastic_2013Riemann

See Also

riem.kmeans

Examples

#-------------------------------------------------------------------
#          Example on Sphere : a dataset with three types
#
# class 1 : 10 perturbed data points near (1,0,0) on S^2 in R^3
# class 2 : 10 perturbed data points near (0,1,0) on S^2 in R^3
# class 3 : 10 perturbed data points near (0,0,1) on S^2 in R^3
#-------------------------------------------------------------------
## GENERATE DATA
mydata = list()
for (i in 1:10){
  tgt = c(1, stats::rnorm(2, sd=0.1))
  mydata[[i]] = tgt/sqrt(sum(tgt^2))
}
for (i in 11:20){
  tgt = c(rnorm(1,sd=0.1),1,rnorm(1,sd=0.1))
  mydata[[i]] = tgt/sqrt(sum(tgt^2))
}
for (i in 21:30){
  tgt = c(stats::rnorm(2, sd=0.1), 1)
  mydata[[i]] = tgt/sqrt(sum(tgt^2))
}
myriem = wrap.sphere(mydata)
mylabs = rep(c(1,2,3), each=10)

## CLRQ WITH K=2,3,4
clust2 = riem.clrq(myriem, k=2)
clust3 = riem.clrq(myriem, k=3)
clust4 = riem.clrq(myriem, k=4)

## MDS FOR VISUALIZATION
mds2d = riem.mds(myriem, ndim=2)$embed

## VISUALIZE
opar <- par(no.readonly=TRUE)
par(mfrow=c(2,2), pty="s")
plot(mds2d, pch=19, main="true label", col=mylabs)
plot(mds2d, pch=19, main="K=2", col=clust2$cluster)
plot(mds2d, pch=19, main="K=3", col=clust3$cluster)
plot(mds2d, pch=19, main="K=4", col=clust4$cluster)
par(opar)

Riemann documentation built on March 18, 2022, 7:55 p.m.