fix: LQ pullback modifies input cotangents (#226)

* make sure LQ pullback does not modify input

* remove unnecessary line

* copy of view to make sure this is copied

* add tests for not modifying output tangents in chainrules

Author: lkdvos

src/pullbacks/lq.jl

@@ -13,8 +13,8 @@ function check_and_prepare_lq_cotangents(
         size(ΔQ) == size(Q) || throw(DimensionMismatch("ΔQ must have the same size as Q"))
         ΔQ₁ .= view(ΔQ, 1:p, 1:n)
         if p == minmn # full rank case, ΔQ₃ contains gauge-invariant information along Q₁
+            ΔQ₃ = copy(view(ΔQ, (minmn + 1):size(Q, 1), :)) # extra columns in the case of qr_full
             Q₃ = view(Q, (minmn + 1):size(Q, 1), :)
-            ΔQ₃ = view(ΔQ, (minmn + 1):size(Q, 1), :)
             ΔQ₃Q₁ᴴ = ΔQ₃ * Q₁'
             mul!(ΔQ₃, ΔQ₃Q₁ᴴ, Q₁, -1, 1)
             Δgauge_Q = norm(ΔQ₃, Inf)

src/pullbacks/qr.jl

@@ -14,8 +14,7 @@ function check_and_prepare_qr_cotangents(
         size(ΔQ) == size(Q) || throw(DimensionMismatch("ΔQ must have the same size as Q"))
         ΔQ₁ .= view(ΔQ, 1:m, 1:p)
         if p == minmn # full rank case, ΔQ₃ contains gauge-invariant information along Q₁
-            ΔQ₃ = ΔQ[:, (minmn + 1):size(Q, 2)] # extra columns in the case of qr_full
-            Q₁ = view(Q, :, 1:minmn)
+            ΔQ₃ = copy(view(ΔQ, :, (minmn + 1):size(Q, 2))) # extra columns in the case of qr_full
             Q₃ = view(Q, :, (minmn + 1):size(Q, 2))
             Q₁ᴴΔQ₃ = Q₁' * ΔQ₃
             mul!(ΔQ₃, Q₁, Q₁ᴴΔQ₃, -1, 1)