Sorting symbols for lambda in alphabetical order

Author: rajithv

lib/symengine.rb

@@ -40,7 +40,7 @@ def evalf_zeta(exp)
         SymEngine::evalf(SymEngine::zeta(exp))
     end
     def lambdify_code(exp)
-      sym_map = exp.free_symbols.map { |sym| sym.to_s}.join(",")
+      sym_map = exp.free_symbols.map { |sym| sym.to_s}.sort.join(",")
       str = exp.to_s
       str.gsub!(/[\d\.]+/, 'Rational(\0,1)')
       replacements = { sin:"Math.sin", cos: "Math.cos", tan: "Math.tan",

spec/lambdify_spec.rb

@@ -5,7 +5,7 @@
   let(:z) { SymEngine::Symbol.new('z') }
 
   it 'creates lambda codes' do
-    expect(SymEngine::lambdify_code( x + y + z )).to eq("lambda { | x,z,y | x + y + z }")
+    expect(SymEngine::lambdify_code( x + y + z )).to eq("lambda { | x,y,z | x + y + z }")
     expect(SymEngine::lambdify_code( x + 5 )).to eq("lambda { | x | Rational(5,1) + x }")
     expect(SymEngine::lambdify_code( SymEngine::sin(x) )).to eq("lambda { | x | Math.sin(x) }")
     expect(SymEngine::lambdify_code( SymEngine::cos(x) )).to eq("lambda { | x | Math.cos(x) }")