fixup #65

its much better to pass the rng via iterator state, otherwise
both identical positions get the same random force thus move
in the same direction. This was messing up an example in the docs

src/sfdp.jl

@@ -76,12 +76,12 @@ function Base.iterate(iter::LayoutIterator{<:SFDP{Dim,Ptype,T}}) where {Dim,Ptyp
     pin = [get(algo.pin, i, SVector{Dim,Bool}(false for _ in 1:Dim)) for i in 1:N]
 
     # iteratorstate: (#iter, energy, step, progress, old pos, pin, stopflag)
-    return startpos, (1, typemax(T), one(T), 0, startpos, pin, false)
+    return startpos, (1, typemax(T), one(T), 0, startpos, pin, rng, false)
 end
 
 function Base.iterate(iter::LayoutIterator{<:SFDP}, state)
     algo, adj_matrix = iter.algorithm, iter.adj_matrix
-    iter, energy0, step, progress, locs0, pin, stopflag = state
+    iter, energy0, step, progress, locs0, pin, rng, stopflag = state
     K, C, tol = algo.K, algo.C, algo.tol
 
     # stop if stopflag (tol reached) or nr of iterations reached
@@ -109,9 +109,7 @@ function Base.iterate(iter::LayoutIterator{<:SFDP}, state)
         end
         if any(isnan, force)
             # if two points are at the exact same location use random force in any direction
-            # copy rng from alg struct to not advance the "initial" rng state
-            # otherwise algo(g)==algo(g) might be broken
-            force += randn(copy(algo.rng), Ftype)
+            force = randn(rng, Ftype)
         end
         mask = (!).(pin[i]) # where pin=true mask will multiply with 0
         locs[i] = locs[i] .+ (step .* (force ./ norm(force))) .* mask
@@ -124,7 +122,7 @@ function Base.iterate(iter::LayoutIterator{<:SFDP}, state)
         stopflag = true
     end
 
-    return locs, (iter + 1, energy, step, progress, locs, pin, stopflag)
+    return locs, (iter + 1, energy, step, progress, locs, pin, rng, stopflag)
 end
 
 # Calculate Attractive force

src/spring.jl

@@ -75,12 +75,12 @@ function Base.iterate(iter::LayoutIterator{<:Spring{Dim,Ptype}}) where {Dim,Ptyp
     pin = [get(algo.pin, i, SVector{Dim,Bool}(false for _ in 1:Dim)) for i in 1:N]
 
     # iteratorstate: #iter nr, old pos, pin
-    return (startpos, (1, startpos, pin))
+    return (startpos, (1, startpos, pin, rng))
 end
 
 function Base.iterate(iter::LayoutIterator{<:Spring}, state)
     algo, adj_matrix = iter.algorithm, iter.adj_matrix
-    iteration, old_pos, pin = state
+    iteration, old_pos, pin, rng = state
     iteration >= algo.iterations && return nothing
 
     # The optimal distance bewteen vertices
@@ -114,9 +114,7 @@ function Base.iterate(iter::LayoutIterator{<:Spring}, state)
             else
                 # if two points are at the exact same location
                 # use random force in any direction
-                # copy rng from alg struct to not advance the "initial" rng state
-                # otherwise algo(g)==algo(g) might be broken
-                force_vec += randn(copy(algo.rng), Ftype)
+                force_vec += randn(rng, Ftype)
             end
 
         end
@@ -134,5 +132,5 @@ function Base.iterate(iter::LayoutIterator{<:Spring}, state)
         locs[i] += force[i] .* scale .* mask
     end
 
-    return locs, (iteration + 1, locs, pin)
+    return locs, (iteration + 1, locs, pin, rng)
 end