Component Guide I: Atomic Components

Overview

Nova models are constructed out of components, which are visual tokens that are placed on the Model Canvas.

To place a component on the model canvas:

• Press the left mouse button on the desired component in the menu obtained from the component tab.
• Drag the component from the component menu onto the model canvas.
• When prompted, provide a component name (a default name will be provided if you choose not to provide one).

A new component requires two actions to integrate it into the model:

• Connections must be made to components with which this component will interact; and
• The new component must be programmed; in the simplest case, this involves providing a component formula that defines the value represented by this component. Specific programming tasks for each component type will be described below.

Component Types

Atomic Components

Tranditional systems dynamic components State (subdivided into Stock Stock+Flow, Sequence, Sequence+Flow, and Store), Flow, and Term; along with Command and Event.

Containers

Nova containers consist of Chips and 5 types of aggregators; a Chip holds a single instance of Capsule, used as a submodel while aggregators hold multiple Capsule instances, possibly of different types. Each aggregator type implements a different topology for its elements. The aggregator components are AgentVector, CellMatrix, NodeNetwork, SimWorld and NetWorld.

Controls and Displays

These include Table, Linechart, Scatterchart, Barchart, Histogram, Slider, Spinner and Toggle.

Special

These are special purpose components consisting of Code Chip and Comment.

Plugins

These are extensions to the component set and have various functions.

Component Properties

Each component has an associated Properties Pane (PropPane) that provides the means for programming the component (and in some cases specifying connections.) The PropPane is opened by selecting the component. PropPanes allow you to define the value represented by a component, set pin connections, determine what is displayed (in the case of Graphs and Tables), calibrate (in the case of Sliders and Spinners) and set any other property required by the component. Specific properties are part of the component descriptions below.

Component Formulas

Most components require a formula or program to specify their values. This formula is a NovaScript expression or sequence of expressions entered into a text area on the PropPane. Component value formulas can make use of the underlying Javascript language to build somewhat complex algorithms for computing the value , however long and complex computations are becodeer relegated to code chips or global method definitions.

Simple Formulas

In the simplest case this will be a constant number or string, or an arithmetic formula. Formulas may reference other value-producing components such as States or Terms, and may also reference any of the global elements known as Primitives.

Examples

Formula	Notes
27
x + 2
2 * PI	PI is a primitive constant.
COS(2*PI*x)	COS is a primitive operator

Important: the caret (^) operator is not supported in Javascript for exponentiation. Instead, use Math.pow; e.g. 2^3 becomes Math.pow(2, 3).

Programmatic Formulas

You may wish to compute the component value over several steps involving conditionals and/or loops. NovaScript permits this according to the following schematic:

statement; statement; .... statement; value

In other words, you may include a sequence of statements, separated by semi-colons, which include local variable declarations and any legal Javascript statement. Numerus will interpret the last entry in that sequence as the value.

Example

var x = 0;
for (var i = 1; i <= 100; i++) x = x + i;
x

This formula will produce 5050

Atomic Components

State

The State component comes in 5 versions.

Symbol	Component	Description
	Stock	A Stock represents a value that is changing over time. Changes to the stock are specified using one or more Flows, which are connected to it. Flows are either inflows or outflows, which respectively represent values being added to or subtracted from the current stock value. The value of a Stock at the end of each time step is equal to the value at the previous time step, plus the total inflow (i.e. the total flow value flowing into the stock) minus the total outflow (i.e., the total flow value flowing out of the stock). Stock values must be numerical.
	Stock+Flow	A stock with a single inflow, for convenience. May be preferred when modeling differential equations.
	Sequence	A Sequence is a type of Stock in which the total flow value replaces rather than adds to the current stock value. A sequence value may be any legal NovaScript data type.
	Sequence+Flow	A sequence with a single inflow, which is generally all that is required.
	Store	A Store is a type of Stock without flows. It is used to hold values that may not require updating at each timestep of the simulation. Stores are used by Commands and Code Chips to store values across simulation timesteps. A Store may be any legal NovaScript data type. Previous versions of Numerus (i.e. Nova 2) called these Local Variables.

Properties

• Initial Value. The initial value is expressed as a component formula.
• Non-Negative. Check this box if the State must be non-negative. Negative values are mapped to 0. This option is not available for Stores.
• Full History. Specifies how long values are retained by this Stock. If selected, values are maintained for the entire length of the simulation; otherwise they are only kept for the previous 100 time units. Check this box only if your simulation requires a longer or complete history of the Stock's value.
• Dimension. Used with Array-Based Modeling.
• Unit. Optional specification of a unit for this State value.

Examples

• 

  Stock

• 

  Stock+Flow

• 

  Sequence

• 

  Sequence+Flow

• 

  Store