# Navigation bar, Expression Builder - Computing systems, networks and telecommunications. Network modeling

## Navigation bar

Using the navigation bar, you can quickly move around different levels of the model, quickly change views. You can specify keyboard shortcuts for changing the view. Kinds of submodels are created automatically, but it is also possible to add new views using the Add View command. You can move not only at different levels of the model, but also quickly get the desired scale of any part of it.

## Expression Builder

Arena PP allows you to build complex expressions. This is achieved using the Expression Builder tool (Figure 2).

Fig. P. 2. Appearance of the expression builder

The expression builder has 3 sections:

1. A window of expression types. Let's consider in more detail the expression types window , which consists of four sections:

1.1. Random Distributions. There are 13 types of standard distributions in the Arena 9.0 PP: normal (normal): Mean, StdDev;

exponential (exponential): Mean;

uniform: Min, Max;

poisson (Poisson): Mean;

gamma (gamma): Beta, Alpha;

beta (beta): Beta, Alpha;

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triangular: Min, Mode, Max;

continious: CumP 1 , Val 1 , ..., CurnP n , Val n ;

discrete: CumP 1 , Val n, ..., CurnP n , Val ";

erlang (Erlang distribution): ExpoMean, to;

johnson (Johnson distribution): Gamma, Delta, Lambda, Xi;

lognormal (lognormal): LogMean, LogStd;

weibull (Weibull distribution): Beta, Alpha.

Let us dwell in more detail on the two types of distributions that are most often used in modeling complex systems. This is the uniform (UNIF or Uniform) and triangular distributions shown in Fig. P. 3, a and 6 respectively. Uniform distribution shows that the probability of occurrence of the event P ↑ is the same (equiprobable) in the interval from Min to Mach, for example, clients come every 5-9 minutes. The triangular distribution shows that the most likely occurrence of the event occurs at some specific time, for example, clients come every 5 to 9 minutes, but often every 7 minutes.

Fig. P. 3. Graphs of the dependencies of distributions: a - uniform distribution: b - triangular distribution

1.2. Math Functions (mathematical functions), which include 11 algebraic operators:

• absolute value;

• rounding to the nearest integer;

• the integer part of a non-integer value;

• the minimum value;

• the maximum value;

• natural logarithm;

• square root, etc., and 9 geometric functions:

• Sine;

• cosine;

• Tangential;

• arcsine, etc.

• Replication Variables (variables associated with model replicas);

• Maximum Replications (maximum number of repetitions);

• Current Replication Number (current number of repetitions).

1.3. Entity-Related Variables:

• Attributes (attributes). The most interesting attributes are Entity.Type (Entity Type), Entity.ScrialNumber (Entity Serial Number), Entity.Picture (Entity Animation Picture), Entity.CreateTime (Entity Creation Time), User-Defined Attribute Value (attributes, specified by the user);

• Group Member Variables (group variables).

1.4. Date and Time Functions. The most interesting and often used operator from this group is TNOW (Current Simulation Time).

2. The panel of operators used in expressions (addition, subtraction, etc., comparison elements, logical operators, etc.).

3. The window for writing an expression.

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