  The subspace Restricted Boltzmann Machine (subspaceRBM) is a third-order
Boltzmann machine where multiplicative interactions are between one visible and
two hidden units. There are two kinds of hidden units, namely, gate units and
subspace units. The subspace units reflect variations of a pattern in data and
the gate unit is responsible for activating the subspace units. Additionally,
the gate unit can be seen as a pooling feature. We evaluate the behavior of
subspaceRBM through experiments with MNIST digit recognition task, measuring
reconstruction error and classification error.
