using namespaces and file paths in php properly

Fatal error: Uncaught Error: Class "MD\model\TodoModel" not found in /var/www/html/app/controller/TodoController.php:7 Stack trace: #0 /var/www/html/app/view/todos/index.php(4): include() #1 {main} thrown in /var/www/html/app/controller/TodoController.php on line 7

<?php
namespace MD\controller;
set_include_path('app/model/');
//require '../model/TodoModel.php';
use MD\model\TodoModel;

class TodoController extends TodoModel {
    public function viewTodos() {
        return $this->selectAllTodos();
    }

    public function add_Todo($todo, $data) {
        return $this->addTodo($todo, $data);
    }

    public function edit_Todo($id) {
        return $this->editTodo($id);
    }

    public function update_Todo($id, $topic, $task) {
        return $this->updateTodo($id, $topic, $task);
    }

    public function delete_Todo($id) {
        return $this->deleteTodo($id);
    }
}