Support tovector and fromvector for even-ordered tensors

src/vector_conversion.jl

@@ -66,26 +66,59 @@ get_params_eltype(::AbstractMaterial) = Float64
 
 # Conversion functions
 """
-    tovector!(v::AbstractVector, m::AbstractMaterial)
+    tovector!(v::AbstractVector, m::AbstractMaterial; offset = 0)
+
 Put the material parameters of `m` into the vector `v`. 
 This is typically used when the parameters should be fitted.
 
-    tovector!(v::AbstractVector, s::AbstractMaterialState)
+    tovector!(v::AbstractVector, s::AbstractMaterialState; offset = 0)
+
 Put the state variables in `s` into the vector `v`.
 This is typically used when differentiating the material 
 wrt. the the old state variables.
+
+    tovector!(v::AbstractVector, a::Union{SecondOrderTensor, FourthOrderTensor}; offset = 0)
+
+Puts the Mandel components of `a` into the vector `v`.
 """
 function tovector! end
 
+# Tensors.jl implementation
+function tovector!(v::AbstractVector, a::SecondOrderTensor; offset = 0)
+    return tomandel!(v, a; offset)
+end
+function tovector!(v::AbstractVector, a::Union{Tensor{4, <:Any, <:Any, M}, SymmetricTensor{4, <:Any, <:Any, M}}; offset = 0) where {M}
+    N = round(Int, sqrt(M))
+    m = reshape(view(v, offset .+ (1:M)), (N, N))
+    tomandel!(m, a)
+    return v
+end
+
 """
-    fromvector(v::AbstractVector, ::MT) where {MT<:AbstractMaterial}
+    fromvector(v::AbstractVector, ::MT; offset = 0) where {MT<:AbstractMaterial}
 Create a material of type `MT` with the parameters according to `v`
 
-    fromvector(v::AbstractVector, ::ST) where {ST<:AbstractMaterialState}
+    fromvector(v::AbstractVector, ::ST; offset = 0) where {ST<:AbstractMaterialState}
 Create a material state of type `ST` with the values according to `v`
+
+    fromvector(v, ::TT; offset = 0) where {TT <: Union{SecondOrderTensor, FourthOrderTensor}}
+
+Create a tensor with shape of `TT` with entries from the Mandel components in `v`.
 """
 function fromvector end
 
+# Tensors.jl implementation
+function fromvector(v::AbstractVector, ::TT; offset = 0) where {TT <: SecondOrderTensor}
+    return frommandel(Tensors.get_base(TT), v; offset)
+end
+
+function fromvector(v::AbstractVector, ::TT; offset = 0) where {TT <: FourthOrderTensor}
+    TB = Tensors.get_base(TT)
+    M = Tensors.n_components(TB)
+    N = round(Int, sqrt(M))
+    return frommandel(TB, reshape(view(v, offset .+ (1:M)), (N, N)))
+end
+
 """
     tovector(m::AbstractMaterial)
 
@@ -108,6 +141,8 @@ function tovector(s::AbstractMaterialState)
     return tovector!(zeros(T, get_num_statevars(s)), s)
 end
 
+tovector(a::Union{SecondOrderTensor, FourthOrderTensor}) = (m = tomandel(a); reshape(m, length(m)))
+
 # Backwards compatibility
 const get_parameter_type = get_params_eltype
 const material2vector! = tovector!

test/TestMaterials.jl

@@ -31,12 +31,12 @@ function MMB.material_response(
 end
 
 MMB.get_num_params(::LinearElastic) = 2
-function MMB.tovector!(v::Vector, m::LinearElastic)
-    v[1] = m.G
-    v[2] = m.K
+function MMB.tovector!(v::Vector, m::LinearElastic; offset = 0)
+    v[1 + offset] = m.G
+    v[2 + offset] = m.K
     return v
 end
-MMB.fromvector(v::Vector, ::LinearElastic) = LinearElastic(v[1], v[2])
+MMB.fromvector(v::Vector, ::LinearElastic; offset = 0) = LinearElastic(v[1 + offset], v[2 + offset])
 
 function MMB.differentiate_material!(
     diff::MaterialDerivatives,

test/runtests.jl

@@ -8,6 +8,7 @@ include("TestMaterials.jl")
 using .TestMaterials
 include("utils4testing.jl")
 
+include("vector_conversion.jl")
 include("stressiterations.jl")
 include("differentiation.jl")
 include("errors.jl")

test/vector_conversion.jl

@@ -0,0 +1,37 @@
+function test_invertible_conversion(x)
+    v1 = tovector(x)
+    # Basic test
+    @test isa(v1, AbstractVector)
+    @test v1 ≈ tovector(fromvector(v1, x))
+
+    # Ensure that we are not using the values in 'x'
+    v2 = rand(length(v1))
+    @test v2 ≈ tovector(fromvector(v2, x))
+
+    # Ensure that offset is working as intended
+    v3 = zeros(length(v1) + 2)
+    r1, r2 = rand(2)
+    v3[1] = r1
+    v3[end] = r2
+    v4 = copy(v3) # Do copy here to keep 2:end-1 filled with zeros
+    tovector!(v3, x; offset = 1)
+    @test v3[1] == r1
+    @test v3[end] == r2
+    @test v3[2:end-1] ≈ v1
+    @test v4 === tovector!(v4, fromvector(v3, x; offset = 1); offset = 1)
+    @test v3 ≈ v4
+end
+
+@testset "vector_conversion" begin
+    @testset "tensors" begin
+        @testset for TT in (Tensor{2,2}, Tensor{4,3}, SymmetricTensor{2,3}, SymmetricTensor{4,2})
+            test_invertible_conversion(rand(TT))
+        end    
+    end
+    @testset "materials" begin
+        @testset for m in (LinearElastic(rand(), rand()),)
+            test_invertible_conversion(m)
+            # TODO: For state variables as well
+        end
+    end
+end