Being an author of books myself on Computer Science text books, I must warn you that all publishers are cheats and none will pay you the royalty earned. When they sell 5000 books, they tell you that they have sold only 500 books and give you the royalty for the same. I had published my books through the best publishers in the field and the situation remains the same. I have discontinued writing books thereafter and do publish my writings as ebook with Amazon. This is just for your information.