What's the legal situation with these academic research papers? Am I allowed to implement an algorithm from a research paper and then either sell the software o

What's the legal situation with these academic research papers? Am I allowed to implement an algorithm from a research paper and then either sell the software or release it as open source? I assume other academics are allowed to reimplement methods in order to reproduce the result and to compare to their own methods. Can I do the same as a learning exercise?