Add remove_dual function

docs/src/DomainBuffers/StateVariables.md

@@ -17,4 +17,5 @@ by its cell number. (The output from the mentioned functions are `Dict{Int}`)
 ```@docs
 FerriteAssembly.create_cell_state
 update_states!
+FerriteAssembly.remove_dual
 ```

docs/src/literate_tutorials/viscoelasticity.jl

@@ -74,10 +74,11 @@ function FerriteAssembly.element_residual!(re, state, ae, m::ZenerMaterial, cv::
             δ∇N = shape_symmetric_gradient(cv, q_point, i)
             re[i] += (δ∇N ⊡ σ) * dΩ
         end
-        ## Note that to save the state by mutation, we need to extract the value from the dual 
-        ## number. Consequently, we do this before assigning to the state vector. Note that 
-        ## if the state was a scalar, we should use `ForwardDiff.value` instead. 
-        state[q_point] = Tensors._extract_value(ϵv)
+        ## We only want to save the value-part of the states, and FerriteAssembly comes with 
+        ## the utility `FerriteAssembly.remove_dual` to do so for scalars and Tensors. 
+        ## Note that using `state[q_point]` instead of ϵv for any calculations 
+        ## affecting re, will result in wrong derivatives.
+        state[q_point] = FerriteAssembly.remove_dual(ϵv)
     end
 end;
 

src/Utils/utils.jl

@@ -1,3 +1,21 @@
+# Public functions for convenience 
+"""
+    remove_dual(x::T) where {T <: Number}
+    remove_dual(x::AbstractTensor{<:Any, <:Any, T}) where {T}
+
+Removes the dual part if `T <: ForwardDiff.Dual`, extract the value part.
+Typically used when assigning state variables during differentiation calls.
+"""
+function remove_dual end
+
+# Scalars
+remove_dual(x::ForwardDiff.Dual) = ForwardDiff.value(x)
+remove_dual(x::Number) = x
+
+# Tensors
+remove_dual(x::AbstractTensor{<:Any, <:Any, <:ForwardDiff.Dual}) = Tensors._extract_value(x)
+remove_dual(x::AbstractTensor) = x
+
 # Internal functions used for convenience
 
 """

test/runtests.jl

@@ -1,4 +1,5 @@
 using Ferrite, FerriteAssembly
+using ForwardDiff
 using SparseArrays
 using Test
 import FerriteAssembly as FA
@@ -46,6 +47,18 @@ include("errors.jl")
         @test FerriteAssembly.get_old_state(buffer, 1) === nothing
 
     end
+
+    @testset "utility functions" begin
+        x = rand()
+        xd = ForwardDiff.Dual(x, rand(3)...)
+        @test x === FerriteAssembly.remove_dual(x)
+        @test x === FerriteAssembly.remove_dual(xd)
+
+        t = rand(Tensor{2,3})
+        td = Tensor{2,3}((i, j) -> ForwardDiff.Dual(t[i, j], rand(), rand()))
+        @test t === FerriteAssembly.remove_dual(t)
+        @test t === FerriteAssembly.remove_dual(td)
+    end
 end
 
 # Print show warning at the end if running tests single-threaded.