Add return level plot for GEV distribution

src/plotrecipes/return_levels.jl

@@ -7,19 +7,25 @@
 
 @recipe function f(rp::ReturnPlot)
  # get user input
- maxima = rp.args[1]
+ obj = rp.args[1]
 
- vals = sort(collect(maxima))
+ if obj isa AbstractMaxima
+ seriestype --> :scatter
+ levels = sort(collect(obj))
+ n = length(levels)
+ p = (1:n) / (n + 1)
+ Δt = 1 ./ (1 - p)
+ elseif obj isa GeneralizedExtremeValue
+ seriestype --> :path
+ a, b = rp.args[2:3]
+ levels = linspace(a, b)
+ Δt = 1 ./ (1 - cdf.(obj, levels))
+ end
 
- n = length(vals)
- p = (1:n) / (n+1)
- T = 1 ./ (1 - p)
-
- seriestype --> :scatter
  xscale --> :log10
  xlabel --> "return period"
  ylabel --> "return level"
- label --> "$n maxima"
+ label --> "return plot"
 
- T, vals
+ Δt, levels
 end