Answers.Body: <p>The abbreviations <em>sim2sim, sim2real</em> and <em>real2real</em> refer to techniques that can be used to transfer knowledge from one environment (e.g. in simulation) to another one (e.g. in the real world).</p>
  
  <ul>
  <li>sim2sim stands for simulation-to-simulation,</li>
  <li>sim2real stands for simulation-to-real, and </li>
  <li>real2real stands for real-to-real. </li>
  </ul>
  
  <p>In sim2sim, knowledge acquired during one simulation is transferred to an agent (or robot) in another simulation. Similarly, in sim2real, knowledge acquired during the simulation is used in a real-world problem (or environment). Finally, in real2real, knowledge acquired in a real-world problem can be transferred to another agent in another real-world problem.</p>
  
  <p>The main challenges are related to the differences that exist between one environment and the other (either in simulation or in the real-world). For example, in <a href="https://arxiv.org/pdf/1812.07252.pdf" rel="nofollow noreferrer">sim2real</a>, the simulation is almost never a perfect model of the real-world environment, so an agent trained in a simulation will probably not behave optimally in the real-world environment, which is often a lot more complex than the simulated environment. However, it is often the case that a robot needs to be trained in simulation, given that a robot trained in a real-world environment is subject to crashes.</p>
  
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Answers.Text: I defined _real2real_ based on the concepts of *sim2sim* and _sim2real_ as used in [Sim-to-Real via Sim-to-Sim: Data-efficient Robotic Grasping via
  Randomized-to-Canonical Adaptation Networks](https://arxiv.org/pdf/1812.07252.pdf) (2019) by Stephen James et al., given that I've not found any paper that uses the expression real2real.
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Body: <p>Recently, I always hear about the terms sim2sim, sim2real and real2real. Will anyone explain the meaning/motivation of these terms (in DL/RL research community)?</p>
  
  <p>What are the challenges in this research area?</p>
  
  <p>Anything intuitive would be appreciated!</p>
  
Tags: <deep-learning><reinforcement-learning><computer-vision><terminology><robotics>
Title: What are sim2sim, sim2real and real2real?
UserDisplayName: wcc
ThreadText: # What are sim2sim, sim2real and real2real?
  
  (Asked by: username_0 on 2019-10-14)
  
  Recently, I always hear about the terms sim2sim, sim2real and real2real. Will anyone explain the meaning/motivation of these terms (in DL/RL research community)?
  
  What are the challenges in this research area?
  
  Anything intuitive would be appreciated!
  
  **Tags:** deep-learning, reinforcement-learning, computer-vision, terminology, robotics
  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_1 on 2019-10-14. Score: 4
  
  The abbreviations *sim2sim, sim2real* and *real2real* refer to techniques that can be used to transfer knowledge from one environment (e.g. in simulation) to another one (e.g. in the real world).
  
  * sim2sim stands for simulation-to-simulation,
  * sim2real stands for simulation-to-real, and
  * real2real stands for real-to-real.
  
  In sim2sim, knowledge acquired during one simulation is transferred to an agent (or robot) in another simulation. Similarly, in sim2real, knowledge acquired during the simulation is used in a real-world problem (or environment). Finally, in real2real, knowledge acquired in a real-world problem can be transferred to another agent in another real-world problem.
  
  The main challenges are related to the differences that exist between one environment and the other (either in simulation or in the real-world). For example, in [sim2real](https://arxiv.org/pdf/1812.07252.pdf), the simulation is almost never a perfect model of the real-world environment, so an agent trained in a simulation will probably not behave optimally in the real-world environment, which is often a lot more complex than the simulated environment. However, it is often the case that a robot needs to be trained in simulation, given that a robot trained in a real-world environment is subject to crashes.
  
  > **Comments:**
  > **username_1**: I defined _real2real_ based on the concepts of *sim2sim* and _sim2real_ as used in [Sim-to-Real via Sim-to-Sim: Data-efficient Robotic Grasping via Randomized-to-Canonical Adaptation Networks](https://arxiv.org/pdf/1812.07252.pdf) (2019) by Stephen James et al., given that I've not found any paper that uses the expression real2real.  
  
  ---
  
  