Decision or Merge Node

Route input tokens based on evaluation of MATLAB expressions, or merge multiple input tokens onto one output flow

Since R2024a

Description

A decision or merge node is represented by a gray diamond. You can use the Decision or Merge Node block for decision or merge functions, depending on how you configure input and output token flows.

Decision node — Consists of only one input token flow, but can have multiple output token flows.
Merge node — Consists of only one output token flow, but can have multiple input token flows.

Decision

The purpose of the decision node is to route incoming tokens, including control flows, to one of the output flows based on the evaluation of boolean expressions associated with each flow. These expressions are called guard expressions. The decision node routes an input token to an output flow if the corresponding guard expression evaluates to true. You can use an incoming token value in a guard expression through the token keyword.

Simple activity diagram with a Merge or Decision node using the token keyword on its output branches.

All guard expressions of a decision node have an evaluation order. The activity diagram editor routes the input token to the first output flow whose guard expression is satisfied. This means that if the value of an incoming object token value satisfies more than one guard expression, it exits through the output branch that is evaluated first.

Merge

The purpose of the merge node is to allow all incoming token flows to exit through a single, common output flow as input tokens arrive at the node.

Decision and Merge

The Decision or Merge Node block can also behave as both a decision and merge node. If you want to use this configuration, you must create the node with multiple input and output flows.

If the node is both a decision and a merge node, then it is equivalent to a merge node immediately followed by a decision node. That is, input object tokens are first merged before routing along the most suitable output flow.

Create a Decision or Merge Node

You can create a decision or merge node on the activity diagram canvas in two ways:

Drag and drop the Decision or Merge Node block from the palette on the left to any location on the canvas.
Hold down the left mouse button at the desired location on the canvas and drag in any direction. A blue outline of a node appears on the canvas. Select Create MergeDecision from the horizontal menu that appears below the outline.

Parameters

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