Figure 3.

VP-local connection infrastructure of NEST. A sparse table (dark orange structure and attached light orange boxes with arrows) holds the thread-local connection objects (pink squares) sorted according to the global index of the associated presynaptic node. The sparse table consists of n_gr equally-sized groups, where each group maintains a bit field (tiny squares) with one bit for each global node index in the group indicating the presence or absence of local targets. If a particular node has local targets, the sparse table stores a pointer to an additional inner data structure (light orange), which has undergone a major redesign during the software development process that led from the 3g to the 4g kernel. (A) Connection infrastructure of the 3g kernel; listed Byte counts contribute to m⁺_c [see Equation (3)]. The inner data structure consists of a vector, which holds a struct for each connection type that the node has locally in use. Each struct links the id of a particular connection type with a pointer to the Connector that stores the connection objects of this type in a vector. (B) Auto-adjusting connection infrastructure of the 4g kernel. Case 1: A particular node has less than K_cutoff local connections and all are of the same type. A lightweight inner structure (HomConnector) stores the connection objects in a fixed-size array. Listed Byte counts contribute to m¹_c. Case 2: A particular node has at least K_cutoff local connections and all are of the same type. A HomConnector stores the connection objects in a dynamically-sized vector. Case 3: The local connections of a particular node are of different types. A HetConnector, which is derived from C++ vector, holds a HomConnector (either Case 1 or 2) for each connection type that the node has locally in use.