Assuming you are training multiple agents in Simulink using the Reinforcement Learning Toolbox in R2020b:
- The rewards are calculated by the environment, not the agent algorithm so they should not be affected unless the environment is changing them. When you compare rewards between single and multi-agents please ensure that the state-action pairs are the same. Rewards depend on states and actions and you may get different results for different state-action pairs.
- In R2020b, the agent neural networks are updated independently.