From 90c2491572f9c45170239e65117908b13bd63826 Mon Sep 17 00:00:00 2001
From: Antoine Marteau <antoine.marteau@protonmail.com>
Date: Mon, 23 Mar 2026 10:55:22 +1100
Subject: [PATCH 1/3] fix SerendipityRefFEs FEEC basis constructor

---
 src/ReferenceFEs/SerendipityRefFEs.jl | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/ReferenceFEs/SerendipityRefFEs.jl b/src/ReferenceFEs/SerendipityRefFEs.jl
index 277e9f1c4..32dc7758e 100644
--- a/src/ReferenceFEs/SerendipityRefFEs.jl
+++ b/src/ReferenceFEs/SerendipityRefFEs.jl
@@ -119,9 +119,8 @@ function compute_monomial_basis(::Type{T},p::SerendipityPolytope{D},orders) wher
 end
 
 function compute_poly_basis(::Type{T},p::SerendipityPolytope{D},orders,poly_type) where {T,D}
-  FEEC_poly_basis
   r = iszero(D) ? 0 : first(orders)
-  FEEC_poly_basis(Val(D),T,r,0,:S,poly_type) # SᵣΛ⁰(□ᴰ)
+  FEEC_poly_basis(Val(D),T,r,0,:S,poly_type; cart_prod=(T <: MultiValue)) # SᵣΛ⁰(□ᴰ)
 end
 
 function compute_own_nodes(p::SerendipityPolytope{0},orders)

From ac3ac62a2d091630ea96c6ac4564dfadc7b550c4 Mon Sep 17 00:00:00 2001
From: Antoine Marteau <antoine.marteau@protonmail.com>
Date: Wed, 1 Apr 2026 17:26:23 +1100
Subject: [PATCH 2/3] fix eltype of LinearCombinationDofVector

e.g. a combination of PointValue cannot be a PointValue
---
 src/ReferenceFEs/Dofs.jl            | 13 ++++++++++---
 test/ReferenceFEsTests/DofsTests.jl |  2 ++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/ReferenceFEs/Dofs.jl b/src/ReferenceFEs/Dofs.jl
index 127ad54d5..b5fdab866 100644
--- a/src/ReferenceFEs/Dofs.jl
+++ b/src/ReferenceFEs/Dofs.jl
@@ -7,6 +7,13 @@ and the range the scalar set.
 """
 abstract type Dof <: Map end
 
+"""
+    struct LinearCombinationDof <: Dof
+
+Type to represent an element of a [`LinearCombinationDofVector`](@ref).
+"""
+struct LinearCombinationDof <: Dof end
+
 """
     struct LinearCombinationDofVector{T<:Dof,V,F} <: AbstractVector{T}
       values :: V
@@ -23,7 +30,7 @@ Fields:
 - `values::AbstractMatrix{<:Number}` the matrix of the change from dof basis (b) to (a)
 - `predofs::AbstractVector{T}` A type representing dof pre-basis (b), with `T<:Dof`
 """
-@ahe struct LinearCombinationDofVector{T,V,F} <: AbstractVector{T}
+@ahe struct LinearCombinationDofVector{T,V,F} <: AbstractVector{LinearCombinationDof}
   values::V
   predofs::F
   function LinearCombinationDofVector(
@@ -46,7 +53,7 @@ end
 
 Base.size(a::LinearCombinationDofVector) = (size(a.values,2),)
 Base.IndexStyle(::LinearCombinationDofVector) = IndexLinear()
-Base.getindex(::LinearCombinationDofVector{T},::Integer) where T = T()
+Base.getindex(::LinearCombinationDofVector,::Integer) = LinearCombinationDof()
 
 function linear_combination(a::AbstractMatrix{<:Number}, b::AbstractVector{<:Dof})
   LinearCombinationDofVector(a,b)
@@ -104,7 +111,7 @@ function Base.getindex(b::ConcatenatedDofVector, i::Integer)
   lengths = length.(bases)
   first_indices = accumulate(+, lengths)
   basis_index = findfirst(>=(i), first_indices)
-  first(bases[basis_index]) # this is PointValue() or Moment() whatever i
+  first(bases[basis_index]) # this is PointValue(..), Moment() or LinearCombinationDof() whatever i
 end
 
 function Arrays.return_cache(b::ConcatenatedDofVector, field)
diff --git a/test/ReferenceFEsTests/DofsTests.jl b/test/ReferenceFEsTests/DofsTests.jl
index f8e20b498..a32eee8e0 100644
--- a/test/ReferenceFEsTests/DofsTests.jl
+++ b/test/ReferenceFEsTests/DofsTests.jl
@@ -3,6 +3,7 @@ module DofsTests
 using Test
 using Gridap
 using Gridap.ReferenceFEs
+using Gridap.ReferenceFEs: LinearCombinationDof
 using Gridap.Fields
 using FillArrays
 
@@ -19,6 +20,7 @@ dofs  = get_dof_basis(reffe0)                  # length 3
 dofs_lc = linear_combination(Eye(3,6), dofs)   # length 6
 @test dofs_lc isa AbstractVector{<:Dof}
 @test length(dofs_lc) == 6
+@test dofs_lc[1] isa LinearCombinationDof
 
 basis = get_prebasis(reffe1)                   # length 4
 @test basis    isa AbstractVector{<:Field}

From 8bcd9af30784580fc1f058136b8cbcbe92b964c0 Mon Sep 17 00:00:00 2001
From: Antoine Marteau <antoine.marteau@protonmail.com>
Date: Wed, 1 Apr 2026 17:33:05 +1100
Subject: [PATCH 3/3] update NEWS.md

---
 NEWS.md | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index a606f988a..3023ccf00 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- The element type of a `LinearCombinationDofVector` is now `LinearCombinationDof`, since PR[#1266](https://github.com/gridap/Gridap.jl/pull/1266).
+
 ## [0.20.3] - 2026-03-23
 
 ### Fixed