common form for negation

Author: ChrisRackauckas

src/simplify.jl

@@ -44,6 +44,8 @@ function _simplify_constants(O)
         end
     elseif O.op == identity
         return O.args[1]
+    elseif Symbol(O.op) == :- && length(O.args) == 1
+        return Operation(*,Expression[-1,O.args[1]])
     else
         return O
     end

test/basic_variables_and_operations.jl

@@ -22,5 +22,3 @@ D*x ~ -σ*(y-x)
 D*y ~ x*(ρ-z)-sin(y)
 
 @test D*t == Constant(1)
-null_op = 0*t
-@test simplify_constants(null_op) == Constant(0)

test/derivatives.jl

@@ -11,7 +11,7 @@ expand_derivatives(dsin)
 
 @test expand_derivatives(dsin) == cos(t)
 dcsch = D*csch(t)
-@test expand_derivatives(dcsch) == Operation(-coth(t)*csch(t))
+@test expand_derivatives(dcsch) == Operation(-1*coth(t)*csch(t))
 # Chain rule
 dsinsin = D*sin(sin(t))
 @test expand_derivatives(dsinsin) == cos(sin(t))*cos(t)
@@ -24,7 +24,7 @@ dpow2 = Derivative(^,[x, y],Val{2})
 d1 = D*(sin(t)*t)
 d2 = D*(sin(t)*cos(t))
 @test expand_derivatives(d1) == t*cos(t)+sin(t)
-@test expand_derivatives(d2) == cos(t)*cos(t)+sin(t)*-sin(t)
+@test expand_derivatives(d2) == cos(t)*cos(t)+sin(t)*(-1*sin(t))
 
 eqs = [0 ~ σ*(y-x),
        0 ~ x*(ρ-z)-y,

test/runtests.jl

@@ -5,5 +5,7 @@ using ModelingToolkit, Base.Test
 @testset "Differentiation Test" begin include("derivatives.jl") end
 @testset "Internal Test" begin include("internal.jl") end
 @testset "Domain Test" begin include("domains.jl") end
+@testset "Simplify Test" begin include("simplify.jl") end
 @testset "Ambiguity Test" begin include("ambiguity.jl") end
+@testset "Componets Test" begin include("components.jl") end
 @testset "System Construction Test" begin include("system_construction.jl") end

test/simplify.jl

@@ -0,0 +1,18 @@
+using ModelingToolkit
+using Base.Test
+
+@IVar t
+@DVar x(t) y(t) z(t)
+
+null_op = 0*t
+@test simplify_constants(null_op) == Constant(0)
+
+one_op = 1*t
+@test simplify_constants(one_op) == t
+
+identity_op = Operation(identity,[x])
+@test simplify_constants(identity_op) == x
+
+minus_op = -x
+@test simplify_constants(minus_op) == -1*x
+simplify_constants(minus_op)