Merge pull request #90 from JuliaDiffEq/fix/export-derivative

Clean up derivatives

Author: ChrisRackauckas

README.md

@@ -269,7 +269,7 @@ t = Parameter(:t)
 x = Unknown(:x, dependents = [t])
 y = Unknown(:y, dependents = [t])
 z = Unknown(:z, dependents = [t])
-D = Differential(t) # Default of first derivative, Derivative(t,1)
+D = Differential(t)
 σ = Parameter(:σ)
 ρ = Parameter(:ρ)
 β = Parameter(:β)

src/differentials.jl

@@ -13,6 +13,7 @@ function (D::Differential)(x::Variable)
     has_dependent(x, D.x) || return Constant(0)
     return Operation(D, Expression[x])
 end
+(::Differential)(::Constant) = Constant(0)
 Base.:(==)(D1::Differential, D2::Differential) = D1.order == D2.order && D1.x == D2.x
 
 function expand_derivatives(O::Operation)
@@ -21,6 +22,7 @@ function expand_derivatives(O::Operation)
     if O.op isa Differential
         D = O.op
         o = O.args[1]
+        isa(o, Operation) || return O
         return simplify_constants(sum(i->Derivative(o,i)*expand_derivatives(D(o.args[i])),1:length(o.args)))
     end
 
@@ -79,4 +81,4 @@ function calculate_jacobian(eqs,vars)
     Expression[Differential(vars[j])(eqs[i]) for i in 1:length(eqs), j in 1:length(vars)]
 end
 
-export Differential, Derivative, expand_derivatives, @Deriv, calculate_jacobian
+export Differential, expand_derivatives, @Deriv, calculate_jacobian

test/basic_variables_and_operations.jl

@@ -3,7 +3,7 @@ using Test
 
 @Param t σ ρ β
 @Unknown x(t) y(t) z(t)
-@Deriv D'~t # Default of first derivative, Derivative(t,1)
+@Deriv D'~t
 @Const c=0
 
 # Default values

test/derivatives.jl

@@ -15,11 +15,6 @@ dcsch = D(csch(t))
 # Chain rule
 dsinsin = D(sin(sin(t)))
 @test expand_derivatives(dsinsin) == cos(sin(t))*cos(t)
-# Binary
-dpow1 = Derivative(^, (x, y), Val(1))
-dpow2 = Derivative(^, (x, y), Val(2))
-@test dpow1 == y*x^(y-1)
-@test dpow2 == x^y*log(x)
 
 d1 = D(sin(t)*t)
 d2 = D(sin(t)*cos(t))
@@ -45,18 +40,8 @@ jac = ModelingToolkit.calculate_jacobian(sys)
 @Unknown a(t) b(a)
 @test D(b) ≠ Constant(0)
 
+@test expand_derivatives(D(x * y)) == simplify_constants(y*D(x) + x*D(y))
+@test_broken expand_derivatives(D(x * y)) == simplify_constants(D(x)*y + x*D(y))
 
-# Regression test for PR #84
-let
-    # Define some variables
-    @Param t σ ρ β
-    @Unknown x(t) y(t) z(t)
-
-    f(x,y,z) = z*x+y
-    # This used to  seg fault, now raises MethodError
-    @test_throws MethodError Derivative(f, x, 1)
-    @Deriv D'~t
-    op = expand_derivatives(D(f(x,y,z)))
-    op.args[1].args[2].name == :z
-    op.args[1].args[2].diff.x.name == :t
-end
+@test expand_derivatives(D(2t)) == 2
+@test expand_derivatives(D(2x)) == 2D(x)

test/system_construction.jl

@@ -4,7 +4,7 @@ using Test
 # Define some variables
 @Param t σ ρ β
 @Unknown x(t) y(t) z(t)
-@Deriv D'~t # Default of first derivative, Derivative(t,1)
+@Deriv D'~t
 @Const c=0
 
 # Define a differential equation