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Neural Random-Access Machines

Paper · 2015 · Karol Kurach, Marcin Andrychowicz and Ilya Sutskever

Summary

Kurach, Andrychowicz and Sutskever (Google) ask whether a neural network can learn pointer-based algorithms, which store addresses, follow them and edit memory, using only input-output pairs and backpropagation. They propose the Neural Random-Access Machine (NRAM). Its trainable controller, a feedforward net or an LSTM, never touches data directly. At each timestep it wires a soft "circuit" from fixed integer modules such as addition, comparisons, min/max, READ and WRITE. Registers and memory cells hold probability distributions over {0,…,M−1}, so any value can serve as a fuzzy address while the whole system stays differentiable. The memory tape also carries the input and receives the output. With curriculum training on synthetic tasks such as Copy, Reverse, Swap, Merge and walking a binary search tree, NRAM learns working procedures on linked lists and trees. For simpler tasks, the learned solutions extend to sequences of any length. The work shows that built-in primitives strongly shape what deep memory-augmented models can learn in practice. It also shows how hard such deep, highly nonlinear models are to optimize.

Key points

  • Architecture: R registers are combined through Q prespecified modules. Module inputs and register updates are softmax-weighted mixtures chosen by the controller. Modules are extended to distributions by summing over all input pairs.
  • Controller input: The controller sees only one scalar per register, the probability that its value is 0. This keeps the parameter count independent of M, which lets the model handle different memory sizes. It also pushes the controller to rely on the modules.
  • Memory: The tape is an M×M probability matrix accessed solely through READ (computed as Mᵀp) and WRITE. The authors note that inference-time memory access can be constant-time under certain assumptions.
  • Tasks and circuits: Tasks include Access, Increment, Copy, Reverse, Swap, Merge and WalkBST. In the extracted circuits, the first timestep handles initialization and later steps repeat one fixed circuit. Swap is the exception, alternating between two circuits on even and odd steps.
  • Training: The curriculum follows Zaremba & Sutskever (2014). Difficulty is sampled uniformly at random 10% of the time, from [1, D+e] 25% of the time, and set to D+e 65% of the time, with e geometric (p = 1/2). The authors report that standard optimizers struggle with these very deep models.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

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Cite

Cite as Karol Kurach, Marcin Andrychowicz and Ilya Sutskever. 2015. Neural Random-Access Machines. arXiv:1511.06392.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.48550/arxiv.1511.06392 · arXiv 1511.06392

@misc{kurach2015neural,
  title = {{Neural Random-Access Machines}},
  author = {Karol Kurach, Marcin Andrychowicz and Ilya Sutskever},
  year = {2015},
  doi = {10.48550/arxiv.1511.06392},
  eprint = {1511.06392},
  archivePrefix = {arXiv},
  url = {https://doi.org/10.48550/arxiv.1511.06392}
}

References

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