SelectOutput

The SelectOutput block routes the incoming agents to one of the two output ports depending on a condition — probabilistic or deterministic. The condition may depend on the agent as well as on any external factors. Agents spend zero time in SelectOutput.

The block can be used to sort agents according to some criteria, to split the agent flow randomly, and so on.

For example, consider agents of type Customer, which has a Boolean field vip. If you want VIP customers to exit the block through the top port (true) and all others through the bottom port (false), specify the condition agent.vip and set Customer as a generic parameter of SelectOutput.

In a more sophisticated case, you might want that only 80% of VIP customers to exit through the top port, and the remaining 20% of VIPs and all other customers to exit through the bottom port. To reflect this, the condition will look like this: agent.vip && randomTrue( 0.8 ).

Sometimes it is necessary to have more than two outputs. AnyLogic provides two blocks for routing agents to different flowchart branches: SelectOutput and SelectOutput5. SelectOutput5 has five output ports, so it can route agents to up to five exits. Using SelectOutputIn and SelectOutputOut blocks you can create a large SelectOutput quasi-block with the required number of exits.

The output port that the agent will take in the SelectOutput block is determined when the agent completes its operation in the preceding flowchart block, not when the agent enters the SelectOutput block. This is necessary because agents do not spend any time in SelectOutput and are immediately forwarded to the next one. Therefore, we need to determine in advance whether the next block can accept the agent.

For example, the next block could be a closed Hold block or a full Queue. The availability of the output route and the output selection are calculated before the agent exits the current block.

By default, the expression that defines the routing condition or an exit number of such a block is evaluated at this earlier point, before the On exit action of the preceding block is executed. As a result, any logic you place in that On exit action (such as changing a custom agent attribute used in the routing condition) will not affect the routing outcome.

To ensure your routing logic works correctly:

• Move any logic that affects routing from the On exit action to the On at exit action, if the block provides one. This action is executed after the block finishes its operation, but before the routing decision is made.
• If this is not possible, insert a Delay block with zero Delay time before the SelectOutput block to separate the change and the routing decision into two steps.
• Alternatively, if your routing logic relies on stochastic or volatile expressions, such as calls of the randomTrue() function or expressions dependent on the current state of other blocks or changes in the agent properties, enable the Condition is stochastic or volatile option in the properties of SelectOutput. By default, this option is disabled: the routing expressions can be evaluated twice, when the agent finishes the operation in the preceding block and when the agent actually leaves the preceding block. If the value of the expression changes between the two evaluations, AnyLogic raises an error, indicating that the agent can no longer follow the initially selected route.
  Enabling the Condition is stochastic or volatile option disables this check, and the agent will follow the route selected during the first evaluation, even if the result of the expression has changed by the time the agent proceeds.

Select True output

Specifies whether agents are routed according to the specified boolean condition (If condition is true) or randomly (With specified probability [0..1]).

Syntax: boolean conditionIsProbabilistic

Probability

[Visible when Select True output: With specified probability]
The expression used to evaluate the probability that the current agent will leave the top port. The probability value should be in the [0..1] range.

Value type: double
Local variable: agent — the agent
Default value: 0.5 — simply splits the agent flow into two equal parts

Condition

[Visible when Select True output: If condition is true]
The condition evaluated for an incoming agent. If it evaluates to true, the agent through the top port, otherwise — through the bottom port.

Value type: boolean
Local variable: agent — the agent
Default value: randomTrue( 0.5 ) — does not depend on the agent and simply splits the agent flow into two equal parts

Condition is stochastic or volatile

[Visible when Select True output: If condition is true]
Specifies that the condition may yield different results when evaluated at different times for the same agent. For example, this may occur if the condition uses random functions or depends on the state of other flowchart blocks.
The condition is checked twice by default: first, when the agent is ready to exit the preceding block and, if the next block was busy and could not accept the agent immediately, possibly again later. A built-in check compares the two evaluations and raises an error if the result has changed.
Enable this option to suppress the check and avoid errors in models where such variability is expected. The final routing decision will be based on the single evaluation that occurs when the agent leaves the preceding block.

Value type: boolean
Default value: false — the condition is assumed to be static between evaluations

On enter

Code executed when the agent enters the block.

Local variable: agent — the agent

On exit (true)

Code executed when the agent exits the block through the upper outT port.

Local variable: agent — the agent

On exit (false)

Code executed when the agent exits the block through the lower outF port.

Local variable: agent — the agent

in

The input port.

outT

The top output port (for the agents, for which the Select condition returned true).

outF

The bottom output port (for the agents, for which the Select condition returned false).

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