Merge pull request #280 from gridap/add_cross_product_for_VectorValues

Added cross product operation for vectors

NEWS.md

@@ -12,6 +12,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - Operator `⊗` (\otimes) as an alias of `outer`. Since PR [#239](https://github.com/gridap/Gridap.jl/pull/239).
   - Support for (symmetric) 4th order tensors. Since PR [#239](https://github.com/gridap/Gridap.jl/pull/239).
   - Optimizations for symmetric 2nd order tensors. Since PR [#239](https://github.com/gridap/Gridap.jl/pull/239).
+  - Methods for `cross` function (aka `×` (\times)) to operate with `VectorValues`.
+  Since PR [#280](https://github.com/gridap/Gridap.jl/pull/280).
 
 ### Changed
 

src/TensorValues/Operations.jl

@@ -260,6 +260,20 @@ end
 
 const ⊗ = outer
 
+###############################################################
+# Cross Product
+###############################################################
+
+function cross(a::MultiValue{Tuple{3}}, b::MultiValue{Tuple{3}})
+  VectorValue{3}(a[2]b[3]-a[3]b[2], a[3]b[1]-a[1]b[3], a[1]b[2]-a[2]b[1])
+end
+
+function cross(a::MultiValue{Tuple{2}}, b::MultiValue{Tuple{2}})
+  a[1]b[2]-a[2]b[1]
+end
+
+cross(a::MultiValue,b::MultiValue) = error("Cross product only defined for R2 and R3 vectors")
+
 ###############################################################
 # Linear Algebra
 ###############################################################
@@ -450,4 +464,3 @@ for op in (:inner,:outer)#,:(:))
         ($op)(a::Function,  b::GridapType) = operate($op,a,b)
     end
 end
-

test/TensorValuesTests/OperationsTests.jl

@@ -263,6 +263,26 @@ c = outer(e,k)
 
 @test tr(c) == VectorValue(50,110)
 
+# Cross product
+
+a = VectorValue(1,2,3)
+b = VectorValue(3,1,6)
+c = VectorValue(9,3,-5)
+@test a × b == c
+
+a = VectorValue(2,3)
+b = VectorValue(5,2)
+@test a × b == -11
+
+a = VectorValue(1.0,5.0,-4.0)
+b = VectorValue(6.0,2.0,3.0)
+c = VectorValue(23.0,-27.0,-28.0)
+@test cross(a, b) == c
+
+a = VectorValue(4.0,1.0)
+b = VectorValue(3.0,-2.0)
+@test cross(a, b) == -11.0
+
 # Linear Algebra
 
 t = TensorValue(10,2,30,4,5,6,70,8,9)