#' Center all particles around the origin without affecting velocity
#'
#' This force repositions the particles at each generation so they are centered
#' around (0,0). It does not affect the velocity of the particles and are thus
#' mainly a guard against the whole body of particles drifting off.
#'
#' @section Training parameters:
#' The following parameters defines the training of the force and can be passed
#' along a call to [wield()]
#'
#' - `x` : The x position to center around (*tidy eval*)
#' - `y` : The y position to center around (*tidy eval*)
#'
#' @family forces
#' @usage NULL
#' @format NULL
#' @export
center_force <- structure(list(
x = NULL,
x_quo = NULL,
y = NULL,
y_quo = NULL,
center_groups = NULL
), class = c('center_force', 'force'))
#' @export
print.center_force <- function(x, ...) {
cat('Center Force:\n')
cat('* A force that keeps all particles centered around the origin\n')
}
#' @export
train_force.center_force <- function(force, particles, x = NULL, y = NULL, ...) {
force <- NextMethod()
force$x_quo <- enquo(x)
force$y_quo <- enquo(y)
nodes <- as_tibble(particles, active = 'nodes')
x <- eval_tidy(force$x_quo, nodes) %||% 0
y <- eval_tidy(force$y_quo, nodes) %||% 0
force$x <- rep(x, length.out = nrow(nodes))
force$y <- rep(y, length.out = nrow(nodes))
force$center_groups <- split(seq_len(nrow(nodes)), paste0(force$x, '-', force$y))
force
}
#' @importFrom rlang quos
#' @importFrom digest digest
#' @export
retrain_force.center_force <- function(force, particles, ...) {
dots <- quos(...)
particle_hash <- digest(particles)
new_particles <- particle_hash != force$particle_hash
if (new_particles) {
force$particle_hash <- particle_hash
nodes <- as_tibble(particles, active = 'nodes')
force <- update_quo(force, 'include', dots, nodes, new_particles, TRUE)
force <- update_quo(force, 'x', dots, nodes, new_particles, 0)
force <- update_quo(force, 'y', dots, nodes, new_particles, 0)
force$center_groups <- split(seq_len(nrow(nodes)), paste0(force$x, '-', force$y))
}
force
}
#' @export
apply_force.center_force <- function(force, particles, pos, vel, alpha, ...) {
for (i in force$center_groups) {
adjust <- colMeans(pos[i, , drop = FALSE]) - c(force$x[i[1]], force$y[i[1]])
center <- matrix(adjust, nrow = length(i), ncol = ncol(pos), byrow = TRUE)
pos[i, ] <- pos[i, , drop = FALSE] - center
}
list(position = pos, velocity = vel)
}
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