An aggregate block will sum (or a similar operation) a selection of other blocks. The aggregate block could be mimicked by an expression block but offers the following advantages:

  • The blocks selected for an aggregate block can be disabled without causing errors in the aggregate (they are simply ignored).
  • The aggregate can be used to create a union of blocks with different sub-sets:

Consider a model with a list of materials. The materials are grouped into two different categories using sub sets.. Organic contaminants belong to the sub-set ‘organic’ wheras the metallic contaminants belong to the sub-set ‘metals’.

The expression ‘C_metal’ computes the concentration in media for the ‘metal’ sub-set. The expression ‘C_organic’ computes the concentration in media for the ‘organic’ sub-set. To create a common expression which collates these two sets of concentrations into one, create an aggregate block with the two blocks C_organic and C_metal.

Creating an aggregate block

From the Projects window

  • Expand the Project to which you wish to add the aggregate by clicking the + symbol next to it. Right-click on ‘Blocks’, or a sub-system in ‘Blocks’, and select Aggregate from the pop-up menu.

From the matrix window

  • Right click an empty diagonal cell of the matrix and select Aggregate from the the pop-up menu.

From the Blocks window

  • Place the mouse anywhere over the area of this window and right-click on it. Select Create | Aggregate from the pop-up menu, or

  • In the title bar, select Aggregate from the Type drop-down list and click on the New button.

Editing an aggregate block

Note Most block properties can be edited directly in the blocks window.

The block editor is shown by right-clicking the block in a window and selecting Edit. In the Blocks window, you can also show the block editor by selecting the block and clicking the Edit button, or by double-clicking the right-most “validation” column of the block.

The block editor has three tabs:


This page lets you edit basic properties such as name, sub-system and base unit. See editing properties for more information.


This page lets you edit the visual properties of the block in the matrix window and graph window. See editing appearance for more information.


This page lets you select the operation to perform and on which blocks to perform it.


  • Operation - Select the operation to perform on the selected blocks.

Dimension - You can specify the dimension of the block by using the Type drop down list. Depending on the dimension the index drop down lists are activated.


Select the blocks to aggregate. You can use the search options in the bottom section to find the blocks you are interested in.

See also