MERLIN is the Multi-task Environments for Reinforcement LearnINg generator. This is a fairly straightforward piece of code that generates random problem instances for a multi-task reinforcement learning agent. The main feature it provides is some controls over the structure of the generated problems, such as the “smoothness” of the transition functions of the underlying MDP, the degree to which the individual tasks are correlated/anti-correlated.

Some preliminary data from this work was presented at the IEEE Symposium on Adaptive Dynamic Programming and Reinforcement Learning (ADPRL-14) in 2014.

Building

Requires python3 and the following packages:

• numpy
• scipy
• networkx

Note that a python3 compatible networkx may be tough to find for your distribution of Linux. There is a debian package available in experimental though which works fine.

Usage

Running python mtlgen.py -h will display a help message, which looks like the following:

usage: mtlgen.py [-h] [--demo] [-t TYPE] [-n STATES] [-m ACTIONS] [-k TASKS]
                 [-c CORRELATION] [-s STDEV] [-x ROWS] [-y COLS]

optional arguments:
  -h, --help            show this help message and exit
  --demo                run with a sample set of parameters
  -t TYPE, --type TYPE  problem instance type {rgudcr,rzcgl}
  -n STATES, --states STATES
                        size of the state space
  -m ACTIONS, --actions ACTIONS
                        number of available actions
  -k TASKS, --tasks TASKS
                        number of concurrent tasks
  -c CORRELATION, --correlation CORRELATION
                        task correlation matrix (in Python nested list form)
  -s STDEV, --stdev STDEV
                        standard deviations of task rewards (in python list
                        form)
  -x ROWS, --rows ROWS  rows in random maze
  -y COLS, --cols COLS  columns in random maze

The most important parameters are the type argument, which specifies what type of problem instance you want to generate. The currently supported options are as follows.

• rgudcr – random graph, uniform out-degree, correlated rewards. This produces problem instances with a given number of states, each of which has exactly the given number of actions available. The problem will have a specified number of separate tasks, and the rewards for each task are real-valued and distributed throughout the entire state-action space, with values that are correlated according to the specified parameters for correlation and standard deviation.

• rzcgl – random maze-like problems, correlated goal locations. These problems are basic 2D gridworld problems with K separate goal states, one for each specified task. The locations of the goal states are related to one another through the specified correlation matrix.