A discrete-event System object™ can contain multiple event types for manipulating entities, acting on the storages, and resource management. When an event is due for execution, a discrete-event system can respond to that event by invoking event actions. The goal of this example is to show how to work with events and event actions when creating a custom block. To see the list of provided event and event actions, see Customize Discrete-Event System Behavior Using Events and Event Actions.
To open the model and to observe the behavior of the custom block, see
In this example, a custom block allows entities to enter its storage element
through its input port. The storage element sorts the entities based on their
Diameter attribute in ascending order. Every entity entry to
the block's storage invokes an iteration event to display the diameter and the
position of each entity in the storage.
The storage element allows you to define its capacity to store and sort entities
during which any entity can be accessed and manipulated. In this example, the
storage with capacity
5 is used to store and sort car wheels
based on their
Diameter attribute in an ascending order. When a
new wheel enters the storage, an iteration event
invoked, which triggers an iteration event action
display wheel positions in the storage and their diameter.
Define a storage with capacity
sorts wheels based in their priority value. The priority values are acquired
Diameter attributes of the entities and are
sorted in ascending order.
function [storageSpecs, I, O] = getEntityStorageImpl(obj) storageSpecs = obj.queuePriority('Wheel',obj.Capacity, 'Diameter','ascending'); I = 1; O = ; end
A wheel's entry into the storage invokes an iterate event.
function [entity, event] = WheelEntry(obj,storage,entity, source) % Entity entry invokes an iterate event. event = obj.eventIterate(1, ''); end
1 is the storage index for the iterate
'' is the tag name.
The iterate event invokes an iterate event action.
% The itarate event action function [entity,event,next] = WheelIterate(obj,storage,entity,tag,cur) % Display wheel id, position in the storage, and diameter. coder.extrinsic('fprintf'); fprintf('Wheel id %d, Current position %d, Diameter %d\n', ... entity.sys.id, cur.position, entity.data.Diameter); if cur.size == cur.position fprintf('End of Iteration \n') end next = true; event=; end
In the code,
coder.extrinsic('fprintf') declares the
fprintf() as extrinsic function for code
generation. For each iteration, the code displays the new wheel ID, current
position, and diameter, which is used as sorting attribute.
.m file as
CustomEntityStorageBlockIteration. Link the
System object to a SimEvents® model by using a MATLAB Discrete-Event
System block. For more information about linking, see Create Custom Blocks Using MATLAB Discrete-Event System Block.
Create a SimEvents model including the MATLAB Discrete-Event System block, and an Entity Generator block.
In the Entity Generator block:
In the Entity type tab, set the
Attribute Name as
Diameter is used to sort entities
in the MATLAB Discrete-Event System block.
In the Event actions tab, in the Generate action field, add this code to randomize the size of the incoming entities.
entity.Diameter = randi([1 10]);
In the Statistics tab, output the Number of entities departed, d statistic and connect to a scope.
Connect the blocks as shown and simulate the model.
Observe that the Entity Generator block generates
5 entities since the capacity of the storage
The Diagnostic Viewer displays the iteration event for each wheel
entry to the storage. Each iteration displays ID, position, and
diameter of the wheels. Observe how each wheel entry changes the
order of the stored wheels. In the last iteration,
5 entities in the storage are sorted in