From f27df6dd26fd5f47e015b6f8de1886093c6b8ed8 Mon Sep 17 00:00:00 2001
From: Antoine Marteau <antoine.marteau@protonmail.com>
Date: Fri, 8 Nov 2024 17:21:44 +1100
Subject: [PATCH 1/4] make evaluate! of AttachDirichletMap type stable

if `mat` and `vec` are real valued and `vals` is complex valued, we still want
to force the `copyto!(vec_with_bcs,vec)` to have a complex valued
return type

fixes #974
---
 src/CellData/AttachDirichlet.jl | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/CellData/AttachDirichlet.jl b/src/CellData/AttachDirichlet.jl
index f38b2cd2d..3e686f238 100644
--- a/src/CellData/AttachDirichlet.jl
+++ b/src/CellData/AttachDirichlet.jl
@@ -70,13 +70,14 @@ function Arrays.return_cache(k::AttachDirichletMap,matvec::Tuple,vals,mask)
 end
 
 function Arrays.evaluate!(cache,k::AttachDirichletMap,matvec::Tuple,vals,mask)
+  mat, vec = matvec
   if mask
-    mat, vec = matvec
     vec_with_bcs = evaluate!(cache,k.muladd,mat,vals,vec)
-    (mat, vec_with_bcs)
   else
-    matvec
+    identity_muladd = MulAddMap(0,1)
+    vec_with_bcs = evaluate!(cache,identity_muladd ,mat,vals,vec)
   end
+  (mat, vec_with_bcs)
 end
 
 function Arrays.return_value(k::AttachDirichletMap,mat,vals,mask)

From d443e8c86a380ce5c852faa5eb9f6208aa0f6e91 Mon Sep 17 00:00:00 2001
From: Antoine Marteau <antoine.marteau@protonmail.com>
Date: Mon, 11 Nov 2024 10:31:50 +1100
Subject: [PATCH 2/4] add MWE of issue 974

---
 test/GridapTests/issue_974.jl | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)
 create mode 100644 test/GridapTests/issue_974.jl

diff --git a/test/GridapTests/issue_974.jl b/test/GridapTests/issue_974.jl
new file mode 100644
index 000000000..2c82250bb
--- /dev/null
+++ b/test/GridapTests/issue_974.jl
@@ -0,0 +1,31 @@
+using Gridap
+
+T = ComplexF64
+
+# Operator creating a linear system where the matrix and RHS are Float64 but the unknown vector is ComplexF64.
+domain = (0, 1, 0, 1)
+partition = (4, 4)
+model = CartesianDiscreteModel(domain, partition)
+
+order = 1
+reffe = ReferenceFE(lagrangian, Float64, order)
+
+V1 = TestFESpace(model, reffe; conformity=:H1, vector_type=Vector{T})
+V2 = TestFESpace(model, reffe; conformity=:H1, vector_type=Vector{T})
+
+U1 = TrialFESpace(V1)
+U2 = TrialFESpace(V2)
+
+Y = MultiFieldFESpace([V1, V2])
+X = MultiFieldFESpace([U1, U2])
+
+degree = 2 * order
+Ω = Triangulation(model)
+dΩ = Measure(Ω, degree)
+
+# Project constant 1 into both spaces.
+a((u1, u2), (v1, v2)) = ∫(v1 * u1)dΩ + ∫(v2 * u2)dΩ
+l((v1, v2)) = ∫(v1 + v2)dΩ
+
+op = AffineFEOperator(a, l, X, Y)
+uh1, uh2 = solve(op)

From e206e08e0fc338f48f8ed66a3664869a95822fcc Mon Sep 17 00:00:00 2001
From: Antoine Marteau <antoine.marteau@protonmail.com>
Date: Fri, 8 Nov 2024 17:28:10 +1100
Subject: [PATCH 3/4] optimization of trivial MulAddMap evaluate!

The (0,1) AttachDirichletMap is just (A,b,c) -> c .

So we can avoid `mul!` in this case (but keep the `copyto!` for type
stability when c is real but b and d=cache[2] are complex).

I believe this is safe regarding type stability since
`return_cache(::AttachDirichletMap)` uses an eager `Base.*` to create
the `cache`, it does not rely on this evaluate.
---
 src/Arrays/AlgebraMaps.jl | 1 +
 src/Fields/ArrayBlocks.jl | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/Arrays/AlgebraMaps.jl b/src/Arrays/AlgebraMaps.jl
index c6bd5144c..546ab393b 100644
--- a/src/Arrays/AlgebraMaps.jl
+++ b/src/Arrays/AlgebraMaps.jl
@@ -35,6 +35,7 @@ function evaluate!(cache,k::MulAddMap,a,b,c)
   setsize!(cache,size(c))
   d = cache.array
   copyto!(d,c)
+  iszero(k.α) && isone(k.β) && return d
   mul!(d,a,b,k.α,k.β)
   d
 end
diff --git a/src/Fields/ArrayBlocks.jl b/src/Fields/ArrayBlocks.jl
index 500fabfc6..12e03a04d 100644
--- a/src/Fields/ArrayBlocks.jl
+++ b/src/Fields/ArrayBlocks.jl
@@ -1281,6 +1281,7 @@ function evaluate!(cache,k::MulAddMap,a::ArrayBlock,b::ArrayBlock,c::ArrayBlock)
   _setsize_mul!(c1,a,b)
   d = evaluate!(c2,unwrap_cached_array,c1)
   copyto!(d,c)
+  iszero(k.α) && isone(k.β) && return d
   mul!(d,a,b,k.α,k.β)
   d
 end
@@ -1517,4 +1518,4 @@ function Base.show(io::IO,o::ArrayBlockView)
 end
 
 LinearAlgebra.diag(a::MatrixBlockView) = view(a.array.array, diag(a.block_map))
-LinearAlgebra.diag(a::MatrixBlock) = view(a.array,diag(CartesianIndices(a.array)))
\ No newline at end of file
+LinearAlgebra.diag(a::MatrixBlock) = view(a.array,diag(CartesianIndices(a.array)))

From 6462fd0e28f09856d63089ded454dce1a5236e9a Mon Sep 17 00:00:00 2001
From: Antoine Marteau <antoine.marteau@protonmail.com>
Date: Mon, 11 Nov 2024 10:48:45 +1100
Subject: [PATCH 4/4] Update NEWS.md

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

diff --git a/NEWS.md b/NEWS.md
index f2973a265..35a4ffd6b 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -5,6 +5,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+### Fixed
+
+- Fixed #974, an error when weak form is real but unknown vector is complex. Since PR[#1050](https://github.com/gridap/Gridap.jl/pull/1050).
+
 ## [0.18.7] - 2024-10-8
 
 ### Added