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

> ### Name: plot_belief_space
> ### Title: Plot a 2D or 3D Projection of the Belief Space
> ### Aliases: plot_belief_space
> ### Keywords: hplot
> 
> ### ** Examples
> 
> # two-state POMDP
> data("Tiger")
> sol <- solve_POMDP(Tiger)
> 
> plot_belief_space(sol)
> plot_belief_space(sol, oneD = FALSE)
> plot_belief_space(sol, n = 10)
> plot_belief_space(sol, n = 100, sample = "random")
> 
> # plot the belief points used by the grid-based solver
> plot_belief_space(sol, sample = sol $solution$belief_points_solver)
> 
> # plot different measures
> plot_belief_space(sol, what = "pg_node")
> plot_belief_space(sol, what = "reward")
> 
> # three-state POMDP
> # Note: If the plotting region is too small then the legend might run into the plot
> data("Three_doors")
> sol <- solve_POMDP(Three_doors)
> sol
POMDP, list - 3-Door Tiger Problem
  Discount factor: 0.75
  Horizon: Inf epochs
  Size: 3 states / 4 actions / 3 obs.
  Start: uniform
  Solved:
    Method: ‘grid’
    Solution converged: TRUE
    # of alpha vectors: 5
    Total expected reward: 5.068327

  List components: ‘name’, ‘discount’, ‘horizon’, ‘states’, ‘actions’,
    ‘observations’, ‘transition_prob’, ‘observation_prob’, ‘reward’,
    ‘start’, ‘info’, ‘solution’
> 
> # plotting needs the suggested package Ternary
> if ("Ternary" %in% installed.packages()) {
+ plot_belief_space(sol)
+ plot_belief_space(sol, n = 10000)
+ plot_belief_space(sol, what = "reward", sample = "random", n = 1000)
+ plot_belief_space(sol, what = "pg_node", n = 10000)
+ 
+ # holding tiger-left constant at .5 follows this line in the ternary plot 
+ Ternary::TernaryLines(list(c(.5, 0, .5), c(.5, .5, 0)), col = "black", lty = 2)
+ # we can plot the projection for this line 
+ plot_belief_space(sol, what = "pg_node", n = 1000, projection = c("tiger-left" = .5))
+ 
+ # plot the belief points used by the grid-based solver
+ plot_belief_space(sol, sample = sol$solution$belief_points_solver, what = "pg_node")
+ 
+ # plot the belief points obtained using simulated trajectories with an epsilon-greedy policy.
+ # Note that we only use n = 50 to save time.
+ plot_belief_space(sol, 
+   sample = simulate_POMDP(sol, n = 50, horizon = 100,
+     epsilon = 0.1, return_beliefs = TRUE)$belief_states)
+ }
Error in check_installed("Ternary") : 
Calls: plot_belief_space -> sample_belief_space -> check_installed
Execution halted