GoldSim 2006 User Conference Slide 1 Vancouver, B.C. Event-Driven Models

GoldSim 2006 User Conference Slide 2 Vancouver, B.C. Continuous-time vs Discrete-event Models GoldSim was originally built as a continuous-time simulator: “Rates of change”, predefined time steps... Gradually more and more discrete-event modeling capabilities have been added: –Timed Event Generator –Discrete Changes –Reservoir overflows –Reliability Failures & Repairs –Etc. etc. These changes have led to a much more complex model-updating logic.

GoldSim 2006 User Conference Slide 3 Vancouver, B.C. Events and Discrete Changes An “Event” is a special type of output that is sent out at discrete times during a simulation. It carries no information other than its occurrence. A “Discrete Change” is like an Event, but it also carries a value and an instruction: “Add” or “Replace”. Events can only connect to a “Trigger” in another element. It’s not their primary purpose, but Discrete Changes can also be used in Triggers.

GoldSim 2006 User Conference Slide 4 Vancouver, B.C. Elements that can Interrupt the Clock The following element types can insert scheduled events that interrupt the model clock: –Timed Event Generator –Reservoir overflow, underflow –Reliability failure time, repair time –Time Series element (discrete changes) –Event Delay –Discrete Change Delay –Fund (interest charges) –Option (on maturity)

GoldSim 2006 User Conference Slide 5 Vancouver, B.C. The Timed Event Generator Comes in five flavors Has Cum_Emitted output

GoldSim 2006 User Conference Slide 6 Vancouver, B.C. Interrupting the Clock The user can disable clock interruption if desired:

GoldSim 2006 User Conference Slide 7 Vancouver, B.C. The Trigger Dialog Comes with five flavors of trigger input. Optionally, after the triggering event, the trigger will wait until a specified condition is true. Optionally, it will then “fire” only if another condition is true.

GoldSim 2006 User Conference Slide 8 Vancouver, B.C. Event-processing Elements Emit only: –Timed Event Generator –Reservoir overflow, underflow Receive only: –Conditional Container –Stochastic Emit & Receive: –Event Delay –Triggered Event Generator –Decision –Random Choice –Milestone –Status –Discrete Change –Reliability –Splitter, Allocator –Option

GoldSim 2006 User Conference Slide 9 Vancouver, B.C. GoldSim’s Updating Process When a model is being edited, GoldSim maintains a ‘causality sequence’ that is used at run time. Links between elements are not made unless a valid causality sequence can be established. Separate, private causality sequences exist for Submodels and for Containers with the ‘Treat as Subsystem’ option selected.

GoldSim 2006 User Conference Slide 10 Vancouver, B.C. Discrete-Change-processing Elements –Discrete Change Generator –Time Series element (discrete changes) –Reservoir –Discrete Change Delay –Splitter, Allocator –Fund (interest charges) –Option (on maturity) –Insurance

GoldSim 2006 User Conference Slide 11 Vancouver, B.C. GoldSim’s Updating Process (simplified) 1.Update static elements in sequence. Supported element types: Data Expression Stochastic Selector Table 2.Update all initial values (inputs must be static). 3.For each time step: 1.Set the clock to the new time. 2.Process any ‘dynamic’ elements that can change with time. 3.Update all function elements in sequence.

GoldSim 2006 User Conference Slide 12 Vancouver, B.C. F10: the Causality Sequence

GoldSim 2006 User Conference Slide 13 Vancouver, B.C. Dynamic Elements These elements have outputs that represent ‘State variables’ for the model. Those outputs are available by any element at any time. This allows such element to reference their own current values, directly or indirectly. Some of those outputs can be hybrids (“Front/Back”), which can change with time and also during the function update. –Elements that reference front/back outputs TRY to sequence after the output, but they don’t have to.

GoldSim 2006 User Conference Slide 14 Vancouver, B.C. Phew!