fix signs

src/backend/mxnet/model.jl

@@ -70,7 +70,7 @@ end
 function Flux.update!(model::MXModel, η)
   for (arg, grad) in zip(model.exec.arg_arrays, model.exec.grad_arrays)
     mx.@nd_as_jl rw = (arg, grad) begin
-      arg .+= grad .* η
+      arg .-= grad .* η
       grad[:] = 0
     end
   end

src/model.jl

@@ -24,7 +24,7 @@ function accumulate!(p::Param, Δ)
 end
 
 function update!(p::Param, η)
-  p.x .+= p.Δx .* η
+  p.x .-= p.Δx .* η
   p.Δx[:] = 0
   return p
 end