Evaluate a pure repulsive layout objective

repulsive.state() evaluates only the repulsion term used by the experimental GMDS repulsive-unfolding operators. Unlike edge.repulsive.state(), this function has no graph-edge term and does not require placeholder edges or edge lengths.

Usage

repulsive.state(
  coords,
  lambda = 1,
  pair.index = NULL,
  pair.weights = NULL,
  repulsion.family = c("log", "inverse_power"),
  repulsion.delta = 0.001,
  repulsion.power = 1,
  distance.eps = 1e-10,
  engine = c("cpp", "R")
)

Arguments

coords

Numeric n by dim coordinate matrix.

lambda

Repulsion strength. The returned total energy is lambda * repel.energy; the gradient is scaled by lambda.

pair.index

Optional two-column matrix of 1-based vertex pairs. If NULL and lambda > 0, all unordered pairs are used.

pair.weights

Optional non-negative pair weights parallel to pair.index.

repulsion.family

Repulsion potential family, either "log" or "inverse_power".

repulsion.delta

Small positive softening parameter for pair distances.

repulsion.power

Power used by the "inverse_power" repulsion.

distance.eps

Small positive distance floor used in derivatives.

engine

Backend engine. "cpp" is the default; "R" uses the reference implementation.

Value

A list containing energy, unscaled repulsion energy, gradient, gradient norm, and embedded pair lengths.

Examples

theta <- seq(0, 2 * pi, length.out = 7)[-7]
coords <- cbind(cos(theta), sin(theta))
state <- repulsive.state(coords, lambda = 0.1, engine = "R")