simplified_expr

Author: ChrisRackauckas

src/ModelingToolkit.jl

@@ -3,6 +3,7 @@ module ModelingToolkit
 export Operation, Expression
 export calculate_jacobian, generate_jacobian, generate_function
 export independent_variables, dependent_variables, parameters
+export simplified_expr
 export @register
 export modelingtoolkitize
 

src/simplify.jl

@@ -75,3 +75,19 @@ function _simplify_constants(O::Operation, shorten_tree)
 end
 _simplify_constants(x, shorten_tree) = x
 _simplify_constants(x) = _simplify_constants(x, true)
+
+function simplified_expr(O::Operation)
+  if O isa Constant
+    return O.value
+  elseif isa(O.op, Differential)
+    return :(derivative($(simplified_expr(O.args[1])),$(simplified_expr(O.op.x))))
+  elseif isa(O.op, Variable)
+    isempty(O.args) && return O.op.name
+    return Expr(:call, Symbol(O.op), simplified_expr.(O.args)...)
+  end
+  return Expr(:call, Symbol(O.op), simplified_expr.(O.args)...)
+end
+
+function simplified_expr(eq::Equation)
+    Expr(:(=), simplified_expr(eq.lhs), simplified_expr(eq.rhs))
+end

test/system_construction.jl

@@ -30,6 +30,20 @@ end
 eqs = [D(x) ~ σ*(y-x),
        D(y) ~ x*(ρ-z)-y,
        D(z) ~ x*y - β*z]
+
+simpexpr = [
+    :(derivative(x(t), t) = σ * (y(t) - x(t)))
+    :(derivative(y(t), t) = x(t) * (ρ - z(t)) - y(t))
+    :(derivative(z(t), t) = x(t) * y(t) - β * z(t))
+    ]
+
+for i in 1:3
+    @test ModelingToolkit.simplified_expr.(eqs)[i].args[1] == simpexpr[i].args[1]
+    @test ModelingToolkit.simplified_expr.(eqs)[i].args[2] == simpexpr[i].args[2].args[2]
+end
+
+ModelingToolkit.simplified_expr.(eqs)[1]
+:(derivative(x(t), t) = σ * (y(t) - x(t))).args
 de = ODESystem(eqs)
 test_diffeq_inference("standard", de, t, (x, y, z), (σ, ρ, β))
 generate_function(de, [x,y,z], [σ,ρ,β])