A pool of nodes is used to limit the search to a beam, rather than traversing the vast space of all possible solutions. We designate the pool at the i-th iteration as .

The nodes are organized in layers, starting from the 0-th layer consisting of the regressor nodes. By , we designate the i-th node in the l-th layer, connected to nodes and  as inputs. By , we denote the i-th layer, being defined as

where n is the number of nodes per layer, i.e. the width of the beam.

The algorithm starts with the pool of nodes empty, and the zeroth layer, a layer of regressor nodes, existing outside the pool.

Then it proceeds to the first iteration.