root_color (#75)

* add root_color interface

* bump version

Author: ranocha

Project.toml

@@ -1,7 +1,7 @@
 name = "RootedTrees"
 uuid = "47965b36-3f3e-11e9-0dcf-4570dfd42a8c"
 authors = ["Hendrik Ranocha <mail@ranocha.de> and contributors"]
-version = "2.9.2"
+version = "2.10.0"
 
 [deps]
 Latexify = "23fbe1c1-3f47-55db-b15f-69d7ec21a316"

src/RootedTrees.jl

@@ -15,7 +15,7 @@ export RootedTree, rootedtree, rootedtree!, RootedTreeIterator,
 
 export butcher_representation
 
-export α, β, γ, density, σ, symmetry, order
+export α, β, γ, density, σ, symmetry, order, root_color
 
 export residual_order_condition, elementary_weight, derivative_weight
 

src/colored_trees.jl

@@ -92,6 +92,13 @@ Base.empty(t::ColoredRootedTree) = ColoredRootedTree(empty(t.level_sequence), em
   return t_dst
 end
 
+"""
+    root_color(t::ColoredRootedTree)
+
+Return the color of the root of `t`.
+"""
+root_color(t::ColoredRootedTree) = first(t.color_sequence)
+
 # Internal interface
 @inline function unsafe_deleteat!(t::ColoredRootedTree, i)
   deleteat!(t.level_sequence, i)
@@ -548,14 +555,14 @@ function butcher_representation(t::ColoredRootedTree, normalize::Bool=true;
   if order(t) == 0
     return "∅"
   elseif order(t) == 1
-    return "τ" * colormap[first(t.color_sequence)]
+    return "τ" * colormap[root_color(t)]
   end
 
   result = ""
   for subtree in SubtreeIterator(t)
     result = result * butcher_representation(subtree, normalize, colormap=colormap)
   end
-  result = "[" * result * "]" * colormap[first(t.color_sequence)]
+  result = "[" * result * "]" * colormap[root_color(t)]
 
   if normalize
     # normalize the result by grouping repeated occurrences of τ

src/time_integration_methods.jl

@@ -194,6 +194,8 @@ end
 # Colored trees are used for order conditions of additive Runge-Kutta methods.
 # The function `color_to_index` maps a color to a one-based index of ARK
 # coefficients.
+# This is considered to be an internal interface but stable across minor/patch
+# releases.
 color_to_index(color::Integer) = Int(color)
 color_to_index(color::Bool) = 1 + color