Added binary operations between Function and FEFunction

Author: fverdugo

src/FESpaces/FEFunctions.jl

@@ -100,16 +100,31 @@ end
 
 for op in (:+, :-, :*)
   @eval begin
+
     function ($op)(a::FEFunction,b::CellField)
       trian = Triangulation(a)
       g = $op(a.cellfield,b)
       _attach_triangulation(g,trian)
     end
+
     function ($op)(a::CellField,b::FEFunction)
       trian = Triangulation(b)
       g = $op(a,b.cellfield)
       _attach_triangulation(g,trian)
     end
+
+    function ($op)(a::FEFunction,b::Function)
+      trian = Triangulation(a)
+      cf = CellField(trian,b)
+      $op(a,cf)
+    end
+
+    function ($op)(a::Function,b::FEFunction)
+      trian = Triangulation(b)
+      cf = CellField(trian,a)
+      $op(cf,b)
+    end
+
   end
 end
 

test/FESpacesTests/FEFunctionsTests.jl

@@ -51,6 +51,12 @@ u = CellField(trian,ufun)
 e = u - uh
 @test isa(e,IndexCellFieldWithTriangulation)
 
+e = ufun - uh
+@test isa(e,IndexCellFieldWithTriangulation)
+
+e = uh - ufun
+@test isa(e,IndexCellFieldWithTriangulation)
+
 T = VectorValue{2,Float64}
 fespace = ConformingFESpace(T,model,order,diritag)
 ufun(x) = VectorValue(x[2],x[1])