Multiple particle system interact with each other

Hi everyone, thank you in advance. I started to learn oF a month ago and I’m studying particle system now. After I read the Mastering Openframeworks and did the example particle system, I want to make multiple particles interact with each other, but I couldn’t figure out how. I also couldn’t find any resources talking about this. What I want to make is like two groups of circles floating around but they rebel each other. Hope for some help!! Thank you!