add check and note in Stiefel transport; add Markus as coauthor; bump version

Author: Jutho

Project.toml

@@ -1,7 +1,7 @@
 name = "TensorKitManifolds"
 uuid = "11fa318c-39cb-4a83-b1ed-cdc7ba1e3684"
-authors = ["Jutho Haegeman"]
-version = "0.4.0"
+authors = ["Jutho Haegeman <jutho.haegeman@ugent.be>", "Markus Hauru <markus@mhauru.org>"]
+version = "0.5.0"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"

src/stiefel.jl

@@ -217,9 +217,12 @@ end
 # not parallel transport for either metric as the corresponding connection has torsion
 # can be computed efficiently: O(np^2) + O(p^3)
 function transport_exp!(Θ::StiefelTangent, W::AbstractTensorMap,
-                        Δ::StiefelTangent, α::Real, W′)
+                        Δ::StiefelTangent, α::Real, W′::AbstractTensorMap)
     W == checkbase(Δ,Θ) || throw(ArgumentError("not a valid tangent vector at base point"))
-    W′, Q, Q′, R′ = stiefelexp(W, Δ.A, Δ.Z, α)
+    # TODO: stiefelexp call does not depend on Θ
+    # cache result or find some other way not to recompute this information
+    _W′, Q, Q′, R′ = stiefelexp(W, Δ.A, Δ.Z, α)
+    W′ ≈ _W′ || throw(ArgumentError("not a valid tangetn vector at end point"))
     A = Θ.A
     Z = Θ.Z
     QZ = Q'*Θ.Z