Merge pull request #1578 from AJ0070/master

Fixed ODE Solver(Test case: 8)

Author: ChrisRackauckas

ext/SymbolicsSymPyExt.jl

@@ -8,20 +8,28 @@ else
     using ..SymPy
 end
 
-using Symbolics: value, symbolics_to_sympy, sympy_to_symbolics
+using Symbolics: value, symbolics_to_sympy, sympy_to_symbolics, Differential, Num
 using SymbolicUtils: iscall, operation, arguments, symtype, FnType, Symbolic, Term
 using LinearAlgebra
 
 function Symbolics.symbolics_to_sympy(expr)
     expr = value(expr)
     expr isa Symbolic || return expr
     if iscall(expr)
-        sop = symbolics_to_sympy(operation(expr))
-        sargs = map(symbolics_to_sympy, arguments(expr))
-        sop === (^) && length(sargs) == 2 && sargs[2] isa Number ? Base.literal_pow(^, sargs[1], Val(sargs[2])) : sop(sargs...)
+        op = operation(expr)
+        args = arguments(expr)
+
+        if op isa Differential
+            @assert length(args) == 1 "Differential operator must have exactly one argument."
+            return SymPy.sympy.Derivative(symbolics_to_sympy(args[1]), symbolics_to_sympy(op.x))
+        end
+
+        sop = symbolics_to_sympy(op)
+        sargs = map(symbolics_to_sympy, args)
+        return sop === (^) && length(sargs) == 2 && sargs[2] isa Number ? Base.literal_pow(^, sargs[1], Val(sargs[2])) : sop(sargs...)
     else
         name = string(nameof(expr))
-        symtype(expr) <: FnType ? SymPy.SymFunction(name) : SymPy.Sym(name)
+        return symtype(expr) <: FnType ? SymPy.SymFunction(name) : SymPy.Sym(name)
     end
 end
 
@@ -89,7 +97,19 @@ function Symbolics.sympy_ode_solve(expr, func, var)
     func_sympy = symbolics_to_sympy(func)
     var_sympy = symbolics_to_sympy(var)
     sol_sympy = SymPy.dsolve(expr_sympy, func_sympy)
-    sympy_to_symbolics(sol_sympy, [func, var])
+    sol_expr = sol_sympy.rhs
+    parsing_vars = Vector{SymbolicUtils.BasicSymbolic}()
+    vars_in_expr = Symbolics.get_variables(value(expr))
+    func_val = value(func)
+    for v in vars_in_expr
+        if !isequal(v, func_val)
+            push!(parsing_vars, v)
+        end
+    end
+    push!(parsing_vars, value(var))
+    push!(parsing_vars, operation(func_val))
+    unwrapped_vars = unique(parsing_vars)
+    sympy_to_symbolics(sol_expr, unwrapped_vars)
 end
 
 end

test/sympy.jl

@@ -65,7 +65,12 @@ result = sympy_simplify(expr)
 @test isequal(Symbolics.simplify(result), 3x^2)
 
 # Test 8: ODE solver
-# D = Differential(x)
-# ode = D(f) - 2*f
-# sol_ode = sympy_ode_solve(ode, f, x)
-# @test isequal(sol_ode, Symbolics.parse("C1*exp(2*x)", Dict("f"=>f, "x"=>x)))
+D = Symbolics.Differential(x)
+@variables C1 
+ode = D(f) - 2*f
+sol_ode = sympy_ode_solve(ode, f, x)
+sol_vars = Symbolics.get_variables(sol_ode)
+const_sym = only(filter(v -> startswith(string(Symbolics.nameof(v)), "C"), sol_vars))
+expected_sol = C1 * exp(2 * x)
+canonical_sol_ode = Symbolics.substitute(sol_ode, Dict(const_sym => C1))
+@test isequal(canonical_sol_ode, expected_sol)