R/056_atoms_elementwise_abs.R

In CVXR: Disciplined Convex Optimization

#####
## DO NOT EDIT THIS FILE!! EDIT THE SOURCE INSTEAD: rsrc_tree/atoms/elementwise/abs.R
#####

## CVXPY SOURCE: atoms/elementwise/abs.py
## Abs -- elementwise absolute value |x|


Abs <- new_class("Abs", parent = Elementwise, package = "CVXR",
  constructor = function(x, id = NULL) {
    if (is.null(id)) id <- next_expr_id()
    x <- as_expr(x)
    shape <- x@shape
    obj <- new_object(S7_object(),
      id    = as.integer(id),
      .cache = new.env(parent = emptyenv()),
      args  = list(x),
      shape = shape
    )
    validate_arguments(obj)
    obj
  }
)

# -- validate: allow complex (CVXPY _allow_complex = True) ------
method(validate_arguments, Abs) <- function(x) {
  ## Abs allows complex arguments; override Elementwise's complex rejection
  invisible(NULL)
}

# -- sign: always nonneg ------------------------------------------
method(sign_from_args, Abs) <- function(x) {
  list(is_nonneg = TRUE, is_nonpos = FALSE)
}

# -- curvature: convex --------------------------------------------
method(is_atom_convex, Abs) <- function(x) TRUE
method(is_atom_concave, Abs) <- function(x) FALSE

# -- monotonicity -------------------------------------------------
method(is_incr, Abs) <- function(x, idx, ...) is_nonneg(x@args[[idx]])
method(is_decr, Abs) <- function(x, idx, ...) is_nonpos(x@args[[idx]])

# -- PWL ----------------------------------------------------------
method(is_pwl, Abs) <- function(x) {
  is_pwl(x@args[[1L]])
}

# -- numeric ------------------------------------------------------
method(numeric_value, Abs) <- function(x, values, ...) {
  abs(values[[1L]])
}

# -- graph_implementation: stub (uses SOCP in CVXPY) --------------
method(graph_implementation, Abs) <- function(x, arg_objs, shape, data = NULL, ...) {
  ## Full graph implementation requires SOCP constraints
  ## For now, stub
  cli_abort("graph_implementation for {.cls Abs} not yet implemented.")
}