Paired Open-Ended Trailblazer (POET): Endlessly Generating Increasingly Complex and Diverse Learning Environments and Their Solutions (1901.01753v3)

Abstract: While the history of machine learning so far largely encompasses a series of problems posed by researchers and algorithms that learn their solutions, an important question is whether the problems themselves can be generated by the algorithm at the same time as they are being solved. Such a process would in effect build its own diverse and expanding curricula, and the solutions to problems at various stages would become stepping stones towards solving even more challenging problems later in the process. The Paired Open-Ended Trailblazer (POET) algorithm introduced in this paper does just that: it pairs the generation of environmental challenges and the optimization of agents to solve those challenges. It simultaneously explores many different paths through the space of possible problems and solutions and, critically, allows these stepping-stone solutions to transfer between problems if better, catalyzing innovation. The term open-ended signifies the intriguing potential for algorithms like POET to continue to create novel and increasingly complex capabilities without bound. Our results show that POET produces a diverse range of sophisticated behaviors that solve a wide range of environmental challenges, many of which cannot be solved by direct optimization alone, or even through a direct-path curriculum-building control algorithm introduced to highlight the critical role of open-endedness in solving ambitious challenges. The ability to transfer solutions from one environment to another proves essential to unlocking the full potential of the system as a whole, demonstrating the unpredictable nature of fortuitous stepping stones. We hope that POET will inspire a new push towards open-ended discovery across many domains, where algorithms like POET can blaze a trail through their interesting possible manifestations and solutions.

Paired Open-Ended Trailblazer (POET) Algorithm

The Paired Open-Ended Trailblazer (POET) algorithm represents a paradigm shift in the approach towards machine learning, where traditional methods typically focus on solving predefined problems. Instead, POET generates not only increasingly challenging learning environments but also the solutions for these evolving challenges. This paper introduces POET as a co-evolutionary framework whereby the exploration of diverse and complex problems occurs in tandem with the optimization of agents tasked with resolving these problems.

Motivation and Approach

The core motivation behind POET is to mimic the open-ended novelty of natural evolution—where complexity grows continually and multiple tasks and solutions co-evolve. Like in nature, where complex behaviors arise gradually through simple, incremental changes and fortuitous crossovers, POET does not rely on a single predefined task space. Instead, new tasks evolve dynamically, allowing for a spontaneous formation of learning curricula where solutions to previous challenges become stepping stones to addressing more difficult problems. This principle of open-ended search deviates from the linear path associated with more traditional curriculum learning frameworks.

Technical Contribution

POET simultaneously evolves two critical components: the environmental challenges and the agents that face these challenges. A unique feature is the constant re-evaluation and transfer of solutions between different environmental niches, enabling knowledge acquired in one context to potentially enhance learning in another. This constant state of flux leads to robust performances on complex tasks, which could not easily be solved through direct optimization or through carefully crafted curriculums. Additionally, POET leverages Evolution Strategies (ES) as its optimization engine, though other reinforcement learning methods could also be applicable.

Results and Comparisons

Experimental studies in a 2-D bipedal walking domain demonstrate POET's efficacy. Observations indicate POET successfully generates and solves complex obstacle courses, significantly surpassing the capabilities of standalone reinforcement learning approaches that commence optimization from scratch—a striking finding since POET-created solutions to challenging environments outperform those generated by direct, isolated efforts with substantial resource allocation. Further, comparisons with curriculum learning controls show that POET's method of evolving environments and transferring solutions results in superior performance. POET fosters a diversity of environments within a single run, a task that remains challenging for controlled curriculum learning.

Implications and Future Directions

POET opens several pathways for enriching machine learning processes. It surpasses the traditional notion of AI problem-solving from labeled datasets by allowing systems to define both their tasks and solutions autonomously, potentially accelerating progress in developing generalizable AI competencies. The implications of POET suggest that instead of finding a single optimal path to problem-solving, a tapestry of potential paths can unlock unforeseen avenues for innovation and discovery.

Looking forward, evolving both agent morphologies and environments could extend the framework's adaptability to more intricate spaces, including dynamically forming challenges in 3-D environments or tailored tasks such as autonomous driving scenarios. Furthermore, integrating POET with advanced forms of indirect encoding and algorithmic diversity, such as Compositional Pattern-Producing Networks (CPPNs), could catalyze further innovation in the morphological and control strategies of AI agents.

In conclusion, the POET framework offers a compelling blend of managed complexity and dynamic evolution, enhancing the capability landscape of artificial intelligence via an open-ended, co-evolutionary approach. The algorithm's unique contribution lies in its potential to self-generate tasks and solutions in perpetuity, promising exciting new horizons for both theoretical exploration and practical application in AI.