Page 601 - ExtendSim User Guide
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Libraries and Blocks 575
Working with blocks
The Constant block has two single input connectors and one single output connector:
A Math block in Add mode has a variable input connector and a single output connector:
The Math block's variable connector expanded to provide three inputs:
Each block's functionality determines whether or not it has variable connectors, where they are located, and what each connector represents. For example, a variable connector could have connectors captioned minimum and maximum placed on the bottom of the block for down- ward expansion.
Variable connectors can be expanded or contracted; they can also be collapsed. You expand or contract a variable connector to provide the desired number of inputs or outputs. You collapse a variable connector to improve model appearance.
Expanding or contracting a variable connector
Wherever possible a block will anticipate its usage and provide the required number of connec- tors. For example, the Holding Tank block (Value library) has a variable connector that can be expanded to provide three inputs: the amount wanted from the tank, a trigger to reset the tank's settings, and the amount of initial contents. You might use one, two, or all three of those inputs, but the block won't allow more than three inputs.
For other blocks, the number of connectors you might need depends on choices you make in the dialog or how you use the block in a model. There are two primary methods for causing a variable connector to change the number of available connectors:
• Dragthevariableconnector(asdiscussedbelow)untilthedesirednumberofconnectorsis achieved. An example of this is the Reservoir model in “, Building a Model ,” where you expanded the variable connector of the Math block (Value library) to two inputs, one each for rainfall and stream. If instead you had six water sources you could have expanded the variable connector to accommodate all six.
• Change some setting in a dialog, causing an increase or decrease in the number of connec- tors. An example of this is the Random Number block (Value library), where you select a distribution from a popup. Depending on the distribution chosen, the variable connector will provide from two to four inputs for specifying the distribution's arguments. Since the num- ber of arguments for each distribution is fixed, you will not be able to expand the number of
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