Adding arrow-type elements

The arrow-type elements are the influence, flow,  squirt and role arrows. In general, arrows link two nodes, though there are exceptions, as explained below. There are two methods of adding arrow-type elements.

1. Click on the required arrow symbol in the tool bar.
2. Drag the mouse from the place where you want the arrow to start, to the place where you want it to end. If you drag outside the model window during this operation, it will be scrolled in that direction bringing more space into view.
3. Repeat (2) if you want to add more arrows of the same type.

Alternatively,

1. Click on the required arrow symbol in the tool bar.
2. Click on the place where you want the arrow to start. The cursor becomes a 'cross-hairs' indicating another click on the diagram is needed to finish adding the link.
3. Click on the place where you want the arrow to end. If you miss the exact point, you can keep the button down and drag to it. If you drag outside the model window during this operation, it will be scrolled in that direction bringing more space into view.
4. Repeat (2) and (3) if you want to add more arrows of the same type.

Note that the button you selected on the tool bar remains depressed until you select another button (i.e. to add a different element, or to change into a different mode, such as label or move). This allows you to add quickly several elements of the same type.

You can also add a single link using either of the methods you would use to add a single node without changing mode, i.e.,

• Drag from the link's toolbar symbol to the start point on the diagram, or
• Right click at the start point to get the context menu, and select "create new" followed by the link type.

Either of these actions sets the cursor to 'cross-hairs', requiring another click to set the end point of the new link.

Specific instructions for each type of arrow

Flow and  squirt arrow

A flow or squirt arrow must:

• begin in a blank area of the screen, and end in a compartment; or
• begin in a compartment, and end in a blank area of the screen; or
• begin in a compartment, and end in a compartment.

Note that if the flow or squirt arrow begins or ends in a blank area of the screen, Simile automatically adds the source/sink symbol (a cloud).

Note also that if you draw two flow arrows between the same two compartments in opposite directions, the arrows mainly lie on top of each other, but the valve (bow-tie or target) symbols are separated. You need to be careful that you know which valve symbol is associated with which arrow, when you come to add influence arrows or equations to the flows. You may like to use the move tool to drag the ends of the flows around one of the compartments to separate them from one another.

Influence arrow

An influence arrow must:

• begin in any model element (except a submodel or an influence arrow); and
• end in any model element (except a submodel or influence arrow).
   

There is an exception to this rule. If you have an influence arrow coming from an input variable inside a submodel to some element (E1); then it is legal to draw an influence arrow from some other element (E2) to this influence arrow. The effect of this is to eliminate the input variable and to cause the influence arrow to go directly from E2 to E1.

Note that if you should accidentally miss the target model element, then the influence arrow will go shooting off to the edge of the model diagram window or submodel boundary. If that happens, then simply click on the undo button in the toolbar, and try again. The reason for this behaviour is to allow you to add placeholders for influence arrows to be taken from submodels. Drag an influence arrow from the placeholder on the submodel boundary, to the desired element outside the submodel to complete the link.

Multiple influences coming from a variable in a submodel to variables outside it will share a common link as far as possible. So will multiple influences coming from a variable outside a submodel to variables inside it. This makes for a much neater diagram when there are lots of influences. However, this can cause odd behaviour when the influences point to variables on opposite sides of the submodel. You can usually fix this by selecting the move tool from the toolbar, and dragging the attachment point around the submodel boundary.

Role arrow

A role arrow must:

• begin in a submodel; and
• end in a submodel.

In: Contents >> Working with model diagrams