4.1. Formation of search tree
Each node in the tree corresponds to a product class. We define nði; jÞ, where i is the last product assigned
and j is the last location assigned to node n. The root node (a dummy starting node at level or stage 0) of the
tree contains no part and allocation to it, i.e., i = 0; j = 0. Subsequent levels or stages (e.g., 1, 2, . . .) in the tree
correspond to the serial number of the class, c. At any node branching is carried out considering all unassigned
parts and enumerating all the possible options. Thus, from node nði; jÞ that were created in stage c 1, one
can generate P i new nodes for the next stage c. Let rðk;mÞ be a node in stage c. Then class c contains part
numbers i + 1 to k and locations j + 1 to m. Note that the number of storage locations required ðm jÞ is
computed using constraint (6). For a class, the allocation based on ranked locations minimizes handling cost
though it may not always result in a regular shape and/or contiguous locations. Let contribution of class c to
the objective function be denoted as hcði þ 1; k; j þ 1;mÞ which can be computed using Eq. (1), given the part
and locations assignment. Let gcðk;mÞ be contribution of classes 1; 2; . . . ; c to the objective function. It is to be
noted that g0ð0; 0Þ is zero. The objective functions of node nði; jÞ at stage c 1 and rðk;mÞ at stage c are related
by