How to reuse algorithms from previous paper In the past, I wrote a paper which included 2 algorithms A and B. Both of them were presented and fully explained. Moreover, B was built based on A, in other words, reader must know about A in order to understand B.

At the moment, I'm writing another paper which further expands B. However, it requires A to be presented (and explained) so that reader can understand. So, I wonder how to present an algorithm A in my new paper. So far, I have 3 solution:


Present and fully explain A in a new paper
Present A and say that its explanation is included in an old paper
State that an algorithm in a new paper in based on algorithm A in an old one, without presenting or explaining it.
You can create a Preliminaries section, and include Algorithm A and its explanation there clearly citing it. That way, it is clear to the reader that the second contains necessary background information, and not new contributions.

As far as how much to include, that really depends on how crucial it is for understanding of expansion of B, how much space you have available, whether the algorithm is published. Any other approaches you suggest are viable.