Merge pull request #16 from MineralsCloud:invariants

Fix src/invariants.jl

Author: singularitti

src/invariants.jl

@@ -8,20 +8,22 @@ principal_values(x::Union{TensorStress,TensorStrain}) = _eigen(x).values
 
 principal_axes(x::Union{TensorStress,TensorStrain}) = _eigen(x).vectors
 
-principal_invariants(x::Union{TensorStress,TensorStrain}) = stress_invariants(parent(x))
+principal_invariants(x::Union{TensorStress,TensorStrain}) = stress_invariants(_tensor(x))
 
 main_invariants(x::Union{TensorStress,TensorStrain}) =
-    deviatoric_stress_invariants(parent(x))
+    deviatoric_stress_invariants(_tensor(x))
 
 for T in (:TensorStress, :TensorStrain)
     @eval begin
-        hydrostatic(x::$T) = $T(vol(SymmetricSecondOrderTensor{3}(float(x))))
-        deviatoric(x::$T) = $T(dev(SymmetricSecondOrderTensor{3}(float(x))))
+        hydrostatic(x::$T) = $T(vol(_tensor(x)))
+        deviatoric(x::$T) = $T(dev(_tensor(x)))
     end
 end
 
+_tensor(x) = SymmetricSecondOrderTensor{3}(float(x))
+
 function _eigen(x)
-    unitless = @. x / oneunit(x)
-    eg = eigen(unitless)
-    return Eigen(eg.values * oneunit(x[1]), eg.vectors)
+    x′ = @. x / oneunit(x)  # Dimensionless
+    eg = eigen(Matrix(x′))
+    return Eigen(eg.values * oneunit(eltype(x)), eg.vectors)
 end