Variables and Parameters

Variables represent values in a calculation, and come in a number of varieties:

Constants

represent an explicit numerical value, and do not have a name. Their graphical representation shows the actual value of the constant.

Parameters

are named constants. All instances of a given name represent the same value, as with all other named variables, so changing the value of one parameter, either through its edit menu, or through a slider, will affect all the others of that name.

Parameters are used to import data from a CSV file, which is how external data is imported into Ravel for analysis.

Parameters can also be used to generate arrays of numbers for use in a Ravel file using built-in formulas which are placed in the ``Initial value'' field of the parameter definition form. See tensor valued initial conditions.

Flow variables

have an input port that defines how the value is to be calculated. Only one flow variable of a given name can have its input port connected, as they all refer to the same quantity. If no input ports are connected, then flow variables act just like parameters.

Integral variables

represent the result of integrating its input over time by means of the differential equation solver. The integrand is represented by the input to an integral operator that is attached to the integral variable.

Stock variables

are the columns of Godley tables, and represent the integral over time of the sum of the flow variables making up the column.

Variables may be converted between types in the variable edit menu, available from the context menu, subject to certain rules. For example, a variable whose input is wired anywhere on the canvas cannot be changed from ``flow''. Stock variables need to be defined in a Godley table, and so on.