Updating record rails 4 No route matches [PATCH] "/admin/usersupdate"

I have this controller

 def usersedit
   @user = User.find_by id: params[:id]
 end

 def usersupdate
   @user = User.find_by id: params[:id]
   if @user.update(post_params)
     redirect_to action: :users
   else
     render 'usersedit'
   end
 end

And this form in the view in usersedit.html.erb

<%= form_for :user, url: {action: "usersupdate"}, method: :patch do |f| %>

but when I submit the form this error appears

No route matches [PATCH] "/admin/usersupdate"

My routes code is:

     Prefix Verb URI Pattern                     Controller#Action
             root GET  /                               pages#home
      admin_index GET  /admin/index(.:format)          admin#index
     admin_grades GET  /admin/grades(.:format)         admin#grades
       pages_home GET  /pages/home(.:format)           pages#home
   pages_register GET  /pages/register(.:format)       pages#register
     pages_create POST /pages/create(.:format)         pages#create
      pages_login GET  /pages/login(.:format)          pages#login
    pages_logging POST /pages/logging(.:format)        pages#logging
     pages_logout GET  /pages/logout(.:format)         pages#logout
                  GET  /activate/:user/:hash(.:format) pages#activate
         remember POST /remember(.:format)             pages#remember
     reactivation POST /reactivation(.:format)         pages#reactivation
  admin_documents GET  /admin/documents(.:format)      admin#documents
      admin_users GET  /admin/users(.:format)          admin#users
                  GET  /admin/usersedit/:id(.:format)  admin#usersedit
admin_usersupdate POST /admin/usersupdate(.:format)    admin#usersupdate

Help please.