Running examples in ‘pomdp-Ex.R’ failed
The error most likely occurred in:

> base::assign(".ptime", proc.time(), pos = "CheckExEnv")
> ### Name: plot_policy_graph
> ### Title: POMDP Plot Policy Graphs
> ### Aliases: plot_policy_graph curve_multiple_directed
> ### Keywords: graphs hplot
> 
> ### ** Examples
> 
> data("Tiger")
> 
> ### Policy graphs for converged solutions
> sol <- solve_POMDP(model = Tiger)
> sol
POMDP, list - Tiger Problem
  Discount factor: 0.75
  Horizon: Inf epochs
  Size: 2 states / 3 actions / 2 obs.
  Start: uniform
  Solved:
    Method: ‘grid’
    Solution converged: TRUE
    # of alpha vectors: 5
    Total expected reward: 1.933439

  List components: ‘name’, ‘discount’, ‘horizon’, ‘states’, ‘actions’,
    ‘observations’, ‘transition_prob’, ‘observation_prob’, ‘reward’,
    ‘start’, ‘info’, ‘solution’
> 
> policy_graph(sol)
IGRAPH 11a6eaa D--- 5 10 -- 
+ attr: label (v/c), id (v/n), action (v/c), size (v/n), label (e/c),
| observation (e/c), arrow.size (e/n)
+ edges from 11a6eaa:
 [1] 1->3 2->3 3->4 4->5 5->3 1->3 2->1 3->2 4->3 5->3
> 
> ## visualization
> plot_policy_graph(sol)
> 
> ## use a different graph layout (circle and manual; needs igraph)
> library("igraph")

Attaching package: ‘igraph’

The following objects are masked from ‘package:stats’:

    decompose, spectrum

The following object is masked from ‘package:base’:

    union

> plot_policy_graph(sol, layout = layout.circle)
> plot_policy_graph(sol, layout = rbind(c(1,1), c(1,-1), c(0,0), c(-1,-1), c(-1,1)), margin = .2)
> plot_policy_graph(sol,
+   layout = rbind(c(1,0), c(.5,0), c(0,0), c(-.5,0), c(-1,0)), rescale = FALSE,
+   vertex.size = 15, edge.curved = 2,
+   main = "Tiger Problem")
> 
> ## hide labels, beliefs and legend
> plot_policy_graph(sol, show_belief = FALSE, edge.label = NA, vertex.label = NA, legend = FALSE)
> 
> ## custom larger vertex labels (A, B, ...)
> plot_policy_graph(sol,
+   vertex.label = LETTERS[1:nrow(policy(sol))],
+   vertex.size = 60,
+   vertex.label.cex = 2,
+   edge.label.cex = .7,
+   vertex.label.color = "white")
> 
> ## plotting the igraph object directly
> pg <- policy_graph(sol, show_belief = TRUE, 
+   simplify_observations = TRUE, remove_unreachable_nodes = TRUE)
> 
> ## (e.g., using a tree layout)
> plot(pg, layout = layout_as_tree(pg, root = 3, mode = "out"))
> 
> ## change labels (abbreviate observations and use only actions to label the vertices)
> plot(pg,
+   edge.label = abbreviate(E(pg)$label),
+   vertex.label = V(pg)$action,
+   vertex.size = 20)
> 
> ## use action to color vertices (requires a graph without a belief pie chart) 
> ##    and color edges to represent observations.
> pg <- policy_graph(sol, show_belief = FALSE, 
+   simplify_observations = TRUE, remove_unreachable_nodes = TRUE)
> 
> plot(pg,
+   vertex.label = NA,
+   vertex.color = factor(V(pg)$action),
+   vertex.size = 20,
+   edge.color = factor(E(pg)$observation),
+   edge.curved = .1
+   )
> 
> acts <- levels(factor(V(pg)$action))
> legend("topright", legend = acts, title = "action",
+   col = igraph::categorical_pal(length(acts)), pch = 15)
> obs <- levels(factor(E(pg)$observation))
> legend("bottomright", legend = obs, title = "observation",
+   col = igraph::categorical_pal(length(obs)), lty = 1) 
> 
> ## plot interactive graphs using the visNetwork library.
> ## Note: the pie chart representation is not available, but colors are used instead.
> plot_policy_graph(sol, engine = "visNetwork")
Error in check_installed("visNetwork") : 
Calls: plot_policy_graph -> .plot.visNetwork -> check_installed
Execution halted
Examples with CPU (user + system) or elapsed time > 5s
           user system elapsed
gridworld 6.199  0.116   7.371