Contents
- Index
Resident variables and constants in MODELS
1. Resident time variables
A number of variables are permanently defined and are available for use in a model. Their value can be used directly in any variable expression of a model, and cannot be modified in assignment statements in the model. Their names are visible in any model, and can be used directly without being declared in a VAR declaration.
The following resident variables provide access to the time characteristics of the simulation of a model. A separate set of values of these variables exists locally for each use of each model. They are:
t the present value of the simulation time in the model;
prevtime the previous value of the simulation time in the model;
timestep the present value of the simulation interval in the model (=t-prevtime);
endtime the external simulation time to which the model is to be updated;
fullstep the total time interval over which the model is to be updated (= endtime - previous endtime);
maxstep the calculated present maximum allowed value of the time step in the model;
minstep the calculated present minimum allowed value of the time step in the model;
Three other resident variables are defined globally for a simulation. They are:
starttime the value of time at the start of the simulation;
stoptime the value of time at which the simulation will end;
startstep the value of the outermost time step at the start of the simulation.
In addition to representing the present value of the simulation time in a model, the variable t can also be used as a regular reference to the value of time in expressions describing history functions in a model (see HISTORY).
2. Resident constants
A number of numerical and logical constants are permanently defined and are available for use in model descriptions. Their value can be used directly in any expression of a model. Their names are visible in any model, and can be used directly without being declared in a CONST declaration.
The following resident constants are defined:
- resident numerical constants:
pi = 3.14159...
inf = very large number fitting the computer in use
undefined = 88888.88888 (value held by any element before it is assigned a first value)
- resident logical constants:
false = 0
true = 1
no = 0
yes = 1
open = 0
closed = 1
off = 0
on = 1