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#' Place nodes using stress majorisation
#'
#' This layout is related to the stress-minimization algorithm known as
#' Kamada-Kawai (available as the 'kk' layout), but uses another optimization
#' strategy. It generally have better runtime, quality, and stability compared
#' to the Kamada-Kawai layout and is thus generally preferred. The sparse
#' version of the layout have better performance (especially on larger networks)
#' at the expense of layout quality, but will generally outperform many other
#' algorithms for large graphs in both runtime and quality (e.g. the 'drl'
#' layout from igraph).
#'
#' @param graph a tbl_graph object
#' @param weights An expression evaluated on the edge data to provide edge
#' weights for the layout. Currently ignored for the sparse version
#' @param pivots The number of pivot nodes.
#' @param niter number of iterations during stress optimization
#' @param tolerance stopping criterion for stress optimization
#' @param mds should an MDS layout be used as initial layout (default: TRUE)
#' @param bbox constrain dimension of output. Only relevant to determine the
#' placement of disconnected graphs.
#' @param circular ignored
#'
#' @return A data.frame with the columns `x`, `y`, `circular` as
#' well as any information stored as node variables in the tbl_graph object.
#'
#' @references
#' Gansner, E. R., Koren, Y., & North, S. (2004). *Graph drawing by stress
#' majorization.* In International Symposium on Graph Drawing (pp. 239-250). Springer, Berlin, Heidelberg.
#'
#' Ortmann, M. and Klimenta, M. and Brandes, U. (2016). *A Sparse Stress Model.* https://arxiv.org/pdf/1608.08909.pdf
#'
#' @family layout_tbl_graph_*
#'
#' @author The underlying algorithm is implemented in the graphlayouts package
#' by David Schoch
#'
#' @importFrom graphlayouts layout_with_stress
#' @importFrom rlang eval_tidy enquo
#'
layout_tbl_graph_stress <- function(graph, weights = NULL, niter = 500,
tolerance = 1e-4, mds = TRUE, bbox = 50,
circular = FALSE) {
weights <- eval_tidy(enquo(weights), .E())
if (is.null(weights)) {
weights <- NA
} else {
weights <- 1 / weights
}
xy <- layout_with_stress(graph, weights = weights, iter = niter,
tol = tolerance, mds = mds, bbox = bbox)
nodes <- data_frame0(x = xy[,1],y = xy[,2], circular = FALSE)
combine_layout_nodes(nodes, as_tibble(graph, active = 'nodes'))
}
#' @rdname layout_tbl_graph_stress
#' @importFrom graphlayouts layout_with_sparse_stress
layout_tbl_graph_sparse_stress <- function(graph, pivots, weights = NULL,
niter = 500, circular = FALSE) {
weights <- eval_tidy(enquo(weights))
if (!is.null(weights)) {
cli::cli_warn('{.arg weights} is currently ignored for sparse stress layouts')
}
xy <- layout_with_sparse_stress(graph, pivots = pivots, weights = weights,
iter = niter)
nodes <- data_frame0(x = xy[,1], y = xy[,2], circular = FALSE)
combine_layout_nodes(nodes, as_tibble(graph, active = 'nodes'))
}
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