comment on rng copy

Author: hexaeder

src/sfdp.jl

@@ -108,8 +108,9 @@ function Base.iterate(iter::LayoutIterator{<:SFDP}, state)
             end
         end
         if any(isnan, force)
-            # if two points are at the exact same location
-            # use random force in any direction
+            # if two points are at the exact same location use random force in any direction
+            # copy rng from alg struct to keep initial random state intact for future invocations
+            # otherwise algo(g)==algo(g) might be broken
             rng = copy(algo.rng)
             force += randn(rng, Ftype)
         end

src/spring.jl

@@ -114,6 +114,8 @@ 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 keep initial random state intact for future invocations
+                # otherwise algo(g)==algo(g) might be broken
                 rng = copy(algo.rng)
                 force_vec += randn(rng, Ftype)
             end