Add simplification for trivial quotients

Author: asterycs

src/forward.jl

@@ -545,6 +545,14 @@ function evaluate(::Mult, arg1::Real, arg2::Zero)
     return evaluate(arg2)
 end
 
+function evaluate(::Div, arg1::Value, arg2::Value)
+    if arg1 == arg2
+        return Literal(1, get_free_indices(arg1)...)
+    end
+
+    return BinaryOperation{Div}(arg1, arg2)
+end
+
 function evaluate(::Add, arg1::Zero, arg2::Zero)
     @assert is_permutation(arg1, arg2)
 

test/ForwardTest.jl

@@ -81,6 +81,23 @@ end
           dc.BinaryOperation{dc.Div}(Variable("x", Upper(2)), l)
 end
 
+@testset "evaluate trivially simplifiable div" begin
+    x = Variable("x", Upper(1))
+    d = KrD(Upper(2), Lower(1))
+
+    function prod(l, r)
+        return dc.BinaryOperation{dc.Mult}(l, r)
+    end
+
+    function div(n, d)
+        return dc.BinaryOperation{dc.Div}(n, d)
+    end
+
+    @test dc.evaluate(div(prod(x, d), prod(x, d))) == Literal(1, Upper(2))
+    @test dc.evaluate(div(prod(x, d), prod(d, x))) == Literal(1, Upper(2))
+    @test dc.evaluate(div(prod(d, x), prod(x, d))) == Literal(1, Upper(2))
+end
+
 @testset "evaluate BinaryOperation{AdditiveOperation} Matrix and KrD" begin
     X = Variable("X", Upper(2), Lower(3))
     d = KrD(Upper(2), Lower(3))