diff --git a/src/containers.jl b/src/containers.jl
index ce0924a..022b83d 100644
--- a/src/containers.jl
+++ b/src/containers.jl
@@ -33,6 +33,15 @@ const NORMAL = Normal()
 struct Strength <: Indexable end
 const STRENGTH = Strength()
 
+#####
+##### dispatch on multipole dimension method
+#####
+abstract type AbstractMethod end
+
+abstract type ScalarPlusVector <: AbstractMethod end
+
+abstract type LambHelmholtz <: AbstractMethod end
+
 #####
 ##### dispatch convenience functions for multipole creation definition
 #####
diff --git a/src/fmm.jl b/src/fmm.jl
index c568564..6ce30e1 100644
--- a/src/fmm.jl
+++ b/src/fmm.jl
@@ -118,7 +118,7 @@ end
 #####
 ##### upward pass
 #####
-function upward_pass_singlethread!(branches, systems, expansion_order::Val{P}) where P
+function upward_pass_singlethread!(branches, systems, expansion_order::Val{P}, ::Type{ScalarPlusVector}) where P
 
     # loop over branches
     for branch in view(branches,length(branches):-1:1) # no need to create a multipole expansion at the very top level
@@ -252,7 +252,7 @@ function translate_multipoles_multithread!(branches, expansion_order::Val{P}, le
     end
 end
 
-function upward_pass_multithread!(branches, systems, expansion_order, levels_index, leaf_index, n_threads)
+function upward_pass_multithread!(branches, systems, expansion_order, levels_index, leaf_index, n_threads, ::Type{ScalarPlusVector})
     # create multipole expansions
     body_2_multipole_multithread!(branches, systems, expansion_order, leaf_index, n_threads)
 
@@ -358,7 +358,7 @@ function nearfield_singlethread!(target_system, target_tree::Tree, derivatives_s
     end
 end
 
-function horizontal_pass_singlethread!(target_branches, source_branches, m2l_list, expansion_order)
+function horizontal_pass_singlethread!(target_branches, source_branches, m2l_list, expansion_order, ::Type{ScalarPlusVector})
     for (i_target, j_source) in m2l_list
         M2L!(target_branches[i_target], source_branches[j_source], expansion_order)
     end
@@ -380,7 +380,7 @@ end
 #     containers = [preallocate_horizontal_pass(expansion_type, expansion_order) for _ in 1:n]
 # end
 
-function horizontal_pass_multithread!(target_branches, source_branches::Vector{<:Branch{TF}}, m2l_list, expansion_order::Val{P}, n_threads) where {TF,P}
+function horizontal_pass_multithread!(target_branches, source_branches::Vector{<:Branch{TF}}, m2l_list, expansion_order::Val{P}, n_threads, ::Type{ScalarPlusVector}) where {TF,P}
     # number of translations per thread
     n_per_thread, rem = divrem(length(m2l_list),n_threads)
     rem > 0 && (n_per_thread += 1)
@@ -420,7 +420,7 @@ function preallocate_l2b(float_type, expansion_type, expansion_order::Val{P}, n_
     return containers
 end
 
-function downward_pass_singlethread!(branches, systems, derivatives_switches, expansion_order::Val{P}) where P
+function downward_pass_singlethread!(branches, systems, derivatives_switches, expansion_order::Val{P}, ::Type{ScalarPlusVector}) where P
     regular_harmonics = zeros(eltype(branches[1].multipole_expansion), 2, (P+1)*(P+1))
     for branch in branches
         if branch.n_branches == 0 # leaf level
@@ -497,7 +497,7 @@ function local_2_body_multithread!(branches, systems, derivatives_switches, expa
     end
 end
 
-function downward_pass_multithread!(branches, systems, derivatives_switch, expansion_order, levels_index, leaf_index, n_threads)
+function downward_pass_multithread!(branches, systems, derivatives_switch, expansion_order, levels_index, leaf_index, n_threads, ::Type{ScalarPlusVector})
     # m2m translation
 	translate_locals_multithread!(branches, expansion_order, levels_index, n_threads)
 
@@ -896,7 +896,7 @@ function fmm!(target_systems, source_systems;
     nearfield=true, farfield=true, self_induced=true,
     unsort_source_bodies=true, unsort_target_bodies=true,
     source_shrink_recenter=true, target_shrink_recenter=true,
-    save_tree=false, save_name="tree", gpu=false
+    save_tree=false, save_name="tree", gpu=false, method=ScalarPlusVector
 )
     # check for duplicate systems
     target_systems = wrap_duplicates(target_systems, source_systems)
@@ -912,7 +912,7 @@ function fmm!(target_systems, source_systems;
         reset_source_tree=false, reset_target_tree=false,
         upward_pass, horizontal_pass, downward_pass,
         nearfield, farfield, self_induced,
-        unsort_source_bodies, unsort_target_bodies, gpu
+        unsort_source_bodies, unsort_target_bodies, gpu, method
     )
 
     # visualize
@@ -960,7 +960,7 @@ function fmm!(systems;
     upward_pass=true, horizontal_pass=true, downward_pass=true,
     nearfield=true, farfield=true, self_induced=true,
     unsort_bodies=true, shrink_recenter=true,
-    save_tree=false, save_name="tree", gpu=false
+    save_tree=false, save_name="tree", gpu=false, method=ScalarPlusVector
 )
     # create tree
     tree = Tree(systems; expansion_order, leaf_size, shrink_recenter)
@@ -971,7 +971,7 @@ function fmm!(systems;
         multipole_threshold, reset_tree=false,
         upward_pass, horizontal_pass, downward_pass,
         nearfield, farfield, self_induced,
-        unsort_bodies, gpu
+        unsort_bodies, gpu, method
     )
 
     # visualize
@@ -1014,7 +1014,7 @@ function fmm!(tree::Tree, systems;
     multipole_threshold=0.4, reset_tree=true,
     upward_pass=true, horizontal_pass=true, downward_pass=true,
     nearfield=true, farfield=true, self_induced=true,
-    unsort_bodies=true, gpu=false
+    unsort_bodies=true, gpu=false, method=ScalarPlusVector
 )
 
     # assemble derivatives switch
@@ -1027,7 +1027,7 @@ function fmm!(tree::Tree, systems;
     fmm!(tree, systems, m2l_list, direct_target_bodies, direct_source_bodies,  derivatives_switches;
         reset_tree,
         nearfield, upward_pass, horizontal_pass, downward_pass,
-        unsort_bodies, gpu
+        unsort_bodies, gpu, method
     )
 
     return m2l_list, direct_target_bodies, direct_source_bodies, derivatives_switches
@@ -1076,7 +1076,7 @@ function fmm!(target_tree::Tree, target_systems, source_tree::Tree, source_syste
     upward_pass=true, horizontal_pass=true, downward_pass=true,
     nearfield=true, farfield=true, self_induced=true,
     unsort_source_bodies=true, unsort_target_bodies=true,
-    gpu=false
+    gpu=false, method=ScalarPlusVector
 )
 
     # assemble derivatives switch
@@ -1089,7 +1089,7 @@ function fmm!(target_tree::Tree, target_systems, source_tree::Tree, source_syste
     fmm!(target_tree, target_systems, source_tree, source_systems, m2l_list, direct_target_bodies, direct_source_bodies, derivatives_switches;
         reset_source_tree, reset_target_tree,
         nearfield, upward_pass, horizontal_pass, downward_pass,
-        unsort_source_bodies, unsort_target_bodies, gpu
+        unsort_source_bodies, unsort_target_bodies, gpu, method
     )
 
     return m2l_list, direct_target_bodies, direct_source_bodies, derivatives_switches
@@ -1123,14 +1123,14 @@ Dispatches `fmm!` using an existing `::Tree`.
 function fmm!(tree::Tree, systems, m2l_list, direct_target_bodies, direct_source_bodies, derivatives_switches;
     reset_tree=true,
     nearfield=true, upward_pass=true, horizontal_pass=true, downward_pass=true,
-    unsort_bodies=true, gpu=false
+    unsort_bodies=true, gpu=false, method=ScalarPlusVector
 )
 
     fmm!(tree, systems, tree, systems, m2l_list, direct_target_bodies, direct_source_bodies, derivatives_switches;
         reset_source_tree=reset_tree, reset_target_tree=false,
         nearfield, upward_pass, horizontal_pass, downward_pass,
         unsort_source_bodies=unsort_bodies, unsort_target_bodies=false,
-        gpu
+        gpu, method
     )
 
 end
@@ -1184,7 +1184,7 @@ function fmm!(target_tree::Tree, target_systems, source_tree::Tree, source_syste
     reset_source_tree=true, reset_target_tree=true,
     nearfield=true, upward_pass=true, horizontal_pass=true, downward_pass=true,
     unsort_source_bodies=true, unsort_target_bodies=true,
-    gpu=false
+    gpu=false, method::Type{<:AbstractMethod}=ScalarPlusVector
 )
     # check if systems are empty
     n_sources = get_n_bodies(source_systems)
@@ -1204,10 +1204,10 @@ function fmm!(target_tree::Tree, target_systems, source_tree::Tree, source_syste
 
             @sync begin
                 Threads.@spawn nearfield_singlethread!(target_systems, direct_target_bodies, derivatives_switches, source_systems, direct_source_bodies, Val(gpu))
-                upward_pass && upward_pass_multithread!(source_tree.branches, source_systems, source_tree.expansion_order, source_tree.levels_index, source_tree.leaf_index, n_threads-1)
-                horizontal_pass && length(m2l_list) > 0 && horizontal_pass_multithread!(target_tree.branches, source_tree.branches, m2l_list, source_tree.expansion_order, n_threads-1)
+                upward_pass && upward_pass_multithread!(source_tree.branches, source_systems, source_tree.expansion_order, source_tree.levels_index, source_tree.leaf_index, n_threads-1, method)
+                horizontal_pass && length(m2l_list) > 0 && horizontal_pass_multithread!(target_tree.branches, source_tree.branches, m2l_list, source_tree.expansion_order, n_threads-1, method)
             end
-            downward_pass && downward_pass_multithread!(target_tree.branches, target_systems, derivatives_switches, target_tree.expansion_order, target_tree.levels_index, target_tree.leaf_index, n_threads)
+            downward_pass && downward_pass_multithread!(target_tree.branches, target_systems, derivatives_switches, target_tree.expansion_order, target_tree.levels_index, target_tree.leaf_index, n_threads, method)
 
         else
 
@@ -1215,16 +1215,16 @@ function fmm!(target_tree::Tree, target_systems, source_tree::Tree, source_syste
             if n_threads == 1 # && !gpu || gpu
 
                 nearfield_singlethread!(target_systems, direct_target_bodies, derivatives_switches, source_systems, direct_source_bodies, Val(gpu))
-                upward_pass && upward_pass_singlethread!(source_tree.branches, source_systems, source_tree.expansion_order)
-                horizontal_pass && length(m2l_list) > 0 && horizontal_pass_singlethread!(target_tree.branches, source_tree.branches, m2l_list, source_tree.expansion_order)
-                downward_pass && downward_pass_singlethread!(target_tree.branches, target_systems, derivatives_switches, target_tree.expansion_order)
+                upward_pass && upward_pass_singlethread!(source_tree.branches, source_systems, source_tree.expansion_order, method)
+                horizontal_pass && length(m2l_list) > 0 && horizontal_pass_singlethread!(target_tree.branches, source_tree.branches, m2l_list, source_tree.expansion_order, method)
+                downward_pass && downward_pass_singlethread!(target_tree.branches, target_systems, derivatives_switches, target_tree.expansion_order, method)
 
             else # n_threads > 1 && !gpu
 
                 nearfield_multithread!(target_systems, direct_target_bodies, derivatives_switches, source_systems, direct_source_bodies, n_threads)
-                upward_pass && upward_pass_multithread!(source_tree.branches, source_systems, source_tree.expansion_order, source_tree.levels_index, source_tree.leaf_index, n_threads)
-                horizontal_pass && length(m2l_list) > 0 && horizontal_pass_multithread!(target_tree.branches, source_tree.branches, m2l_list, source_tree.expansion_order, n_threads)
-                downward_pass && downward_pass_multithread!(target_tree.branches, target_systems, derivatives_switches, target_tree.expansion_order, target_tree.levels_index, target_tree.leaf_index, n_threads)
+                upward_pass && upward_pass_multithread!(source_tree.branches, source_systems, source_tree.expansion_order, source_tree.levels_index, source_tree.leaf_index, n_threads, method)
+                horizontal_pass && length(m2l_list) > 0 && horizontal_pass_multithread!(target_tree.branches, source_tree.branches, m2l_list, source_tree.expansion_order, n_threads, method)
+                downward_pass && downward_pass_multithread!(target_tree.branches, target_systems, derivatives_switches, target_tree.expansion_order, target_tree.levels_index, target_tree.leaf_index, n_threads, method)
             end
 
         end
diff --git a/test/runtests.jl b/test/runtests.jl
index 753d822..aea076a 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -22,7 +22,7 @@ include(joinpath(test_dir, "gravitational.jl"))
 # allow expansion_order::Int to be used while testing
 FastMultipole.M2M!(branch, child, harmonics, M, expansion_order::Int) = FastMultipole.M2M!(branch, child, harmonics, M, Val(expansion_order))
 FastMultipole.M2L!(target_branch, source_branch, harmonics, L, expansion_order::Int) = FastMultipole.M2L!(target_branch, source_branch, harmonics, L, Val(expansion_order))
-FastMultipole.upward_pass_singlethread!(branches, systems, expansion_order::Int) = FastMultipole.upward_pass_singlethread!(branches, systems, Val(expansion_order))
+FastMultipole.upward_pass_singlethread!(branches, systems, expansion_order::Int) = FastMultipole.upward_pass_singlethread!(branches, systems, Val(expansion_order), FastMultipole.ScalarPlusVector)
 FastMultipole.M2L!(target_branch, source_branch, expansion_order::Int) = FastMultipole.M2L!(target_branch, source_branch, Val(expansion_order))
 
 @testset "complex" begin
@@ -568,7 +568,7 @@ u_fmm_67 = mass_target_potential[1]
 # perform horizontal pass
 m2l_list, direct_list_target, direct_list_source = FastMultipole.build_interaction_lists(tree.branches, tree.branches, tree.leaf_index, multipole_threshold, true, true, true)
 FastMultipole.nearfield_singlethread!((elements,), direct_list_target, (FastMultipole.DerivativesSwitch(),), (elements,), direct_list_source)
-FastMultipole.horizontal_pass_singlethread!(tree.branches, tree.branches, m2l_list, expansion_order)
+FastMultipole.horizontal_pass_singlethread!(tree.branches, tree.branches, m2l_list, expansion_order, FastMultipole.ScalarPlusVector)
 
 # consider the effect on branch 3 (mass 2)
 elements.potential[i_POTENTIAL,new_order_index[2]] .*= 0 # reset potential at mass 2