Fixes Nested PowerManifold of a PowerManifold to not concatenate size…

…s. (#235)

* specify that Nested of a Powermanifold yields a powermanifold within a powermanifold and does not concatenate sizes.

src/manifolds/PowerManifold.jl

@@ -69,6 +69,8 @@ dimensions will be appended to the dimensions already present, for example
 `PowerManifold(PowerManifold(Sphere(2), 2), 3)` is equivalent to
 `PowerManifold(Sphere(2), 2, 3)`. This feature preserves the representation of the inner
 power manifold (unless it's explicitly overridden).
+If you specify `NestedPowerRepresentation()`, the sizes are not concatenated but you end up
+with a nested power manifold within a power manifold.
 """
 struct PowerManifold{𝔽,TM<:Manifold{𝔽},TSize,TPR<:AbstractPowerRepresentation} <:
        AbstractPowerManifold{𝔽,TM,TPR}
@@ -98,7 +100,20 @@ function PowerManifold(
 ) where {𝔽,TM<:Manifold{𝔽},TSize,TPR<:AbstractPowerRepresentation}
     return PowerManifold{𝔽,TM,Tuple{TSize.parameters...,size...},TPR}(M.manifold)
 end
-
+function PowerManifold(
+    M::PowerManifold{𝔽,TM,TSize},
+    ::NestedPowerRepresentation,
+    size::Integer...,
+) where {𝔽,TM<:Manifold{𝔽},TSize}
+    return PowerManifold{
+        𝔽,
+        PowerManifold{𝔽,TM,TSize},
+        Tuple{size...},
+        NestedPowerRepresentation,
+    }(
+        M,
+    )
+end
 @doc raw"""
     PowerMetric <: Metric
 

test/power_manifold.jl

@@ -15,6 +15,10 @@ Random.seed!(42)
     Ms2 = PowerManifold(Ms, 5, 7)
     @test power_dimensions(Ms2) == (5, 7)
     @test manifold_dimension(Ms2) == 70
+    Ms2n = PowerManifold(Ms1, NestedPowerRepresentation(), 7)
+    @test power_dimensions(Ms2n) == (7,)
+    @test manifold_dimension(Ms2n) == 70
+
     Mr = Manifolds.Rotations(3)
     Mr1 = PowerManifold(Mr, 5)
     Mrn1 = PowerManifold(Mr, Manifolds.NestedPowerRepresentation(), 5)