GB1293494A - The analysis of networks having nodes interconnected by vectors - Google Patents

Abstract

1293494 Critical path analysis SOC NATIONALE D'ETUDE ET DE CONSTRUCTION DE MOTEURS D'AVIATION 1 June 1971 [1 June 1970] 18482/71 Heading G4A A network comprising a number of nodes interconnected by meshes or links is evaluated e.g. for critical path using a network modelling circuit. The network may be of the form shown in Fig. 1 having nodes A-F, A being called a starting point node and D being a target point node. The links between nodes can be weighted, i.e. the time taken to go between C and D is four times that between E and B and twice that between E and F &c. It is desired to find the critical path, that is the longest path between the starting and target nodes, which in Fig. 1 is along the path AEFCD. Logic circuits are provided having node elements and link elements representing the nodes and links of the network and the network paths are simulated by transmitting signals which advance stepwise between consecutive node elements (taking any weighting into account) in a similar manner to British Specification 1,173,796. The apparatus, Fig. 5.-A typical link M of the circuit has a predecessor node Np and a successor node Ns, and M, Np and Ns have elements in three chains. # Connections are responsible for transferring critical path finding signals from the target to the starting point nodes. This is known as # backwards finding and, upon completion thereof, γ connections transfer a signal from the starting point node via links forming part of the critical path to the target. α Connections are used for selecting links suitable for path finding before it commences, and thus locating loops in the network, e.g. for display. Each node has an AND gate 1 having n inputs on the # chain where n denotes the number of links extending from the node and the output of the gate goes to AND gate 3 in the link M which transmits clock pulses from a generator to a backwards counter D31. At the start of path finding the counter is set to a value equal to the weighting in the link, # signals are transmitted from the target and the counter counts back 1 for each clock pulse until it reaches 0 when Np is energized. Np only passes the signal when all the counters connected thereto are zero and means note which counter reached zero last (i.e. which link is in the critical path). The γ connections are only enabled if the counters are at 0. The path length is determined by counting the number of clock pulses between the sending of # signals from the target and the arrival of a # signal at the start. When all the counters are set to 0 the γ signal travels back along a path other than the longest and the critical path is then displayed or recorded by sampling at S 4 or S 12 and showing the link element or node element outputs. Where two critical paths are the same length a hierarchy system (line 61) can choose one, and the system can be modified by automatically or manually inhibiting a link. A number of problems can be solved using the γ, #, α connections, e.g. determining and displaying all paths connecting any start to any target and, with a few modifications, can be used to find the shortest path between two nodes (Figs. 9 and 10, not shown).