2.3.1.1  System

System parameters are shown in Table 1:

Table 1. System parameters

In this table, the column Parameter lists system parameters by name, the column No contains the identifier of the detailed description. The column Type shows the parameter type (in C language), font is for the types to store a character set each, and color is for the types to store a color each. The Control type shows the relevant control type in the dialog window.

Figure 1, Figure 2, Figure 3 and Figure 4 show details in the windows of changing system parameters, including illustrative data. The numbers in small circles are identifiers of the detailed descriptions:

Figure 1. The page System in the dialog window Create new system/System properties

Figure 2. The page Visuals in the dialog window Create new system/System properties

Figure 3. The page Other (system) in the dialog window Create new system/System properties

Figure 4. The page Description in the dialog window Create new system/System properties

2.3.1.1.1  System name

To be given as compulsory, the name of the System shall be minimum 1 or maximum 32 characters long. The name of the system is not identical to the name of Gravity file of .grav extension (see Description of the grav file), which is to store the system (and related bodies and groups). This name also appears in the window header.

2.3.1.1.2  Gravitational constant multiplicator

This is the multiplier of the gravitation constant . The value of the gravitation constant itself is changed in the dialog window Default properties. It is a number of double¹ type, cannot be zero or less.

2.3.1.1.3  Time unit

On this basis, the model will compute a new position for each body. It's an unreal time. If, for instance, one hour is specified as time unit, then the program will compute where bodies would be after one hour in reality, but the result may occur in fraction of a second. The lesser it is, the more precise modeling, but at the same time, the slower the simulation is. It is a number of double type, cannot be zero or less.

2.3.1.1.4  Screen refresh time

Screen refresh time defines the interval, in which the screen shall be refreshed. It's an unreal time. If this value is 10 times higher than the Time unit and the Time unit type is static, then the results of every tenth computations will appear on the screen. A higher value may result in a fast, but less continuous simulation. It is a number of double type, cannot be less, then the Time unit.

2.3.1.1.5  Simulation length

The Simulation length defines how long the simulation shall be. The 0 default value means a time of unlimited length, where running will not end automatically.

For instance, suppose Time unit type static, Time unit 1s, Screen refresh time 2s, Simulation length 4s, and Repeat off. If so, the result of the second and forth computing will appear on the screen, and then simulation will automatically stop. It makes sense of Simulation length and Repeat together: a process may be automatically played back several times, while parameters might change. If this value is other than zero, then shall not be less, than Screen Refresh. It is a number of double type.

2.3.1.1.6  Zoom

Zooming is dealt with in the section Zoom. It is a number of double type, cannot be zero or less.

2.3.1.1.7  Character sets for the background and mouse pointer

Body and group name appear on the screen with the background character set. In the Mouse pointer (below the crosshair) text information may appear with the mouse pointer character set. Defaults for character sets may be set in the dialog window Default properties.

2.3.1.1.8  Dimensional units

Here, the System-related dimensional units are set. Defaults for dimensional are set in the dialog window Default properties.

2.3.1.1.9  Time unit type

The time unit type may be static or dynamic. For static type, the Time unit does not change automatically during simulation. In the dynamic case, the program is able to change time unit automatically during simulation. If a body gets so near to another that after the time unit elapsed, its position would change better than the Proximity rate of the other body's distance, than the time unit will reduce as follows:

Suppose the move of body A is np after dt time elapsed, the distance between body A and B is di, the proximity is 100, then dp = di / 100.

If during the simulation, two bodies get near to each other that is the condition np < dp, then the time unit is multiplied by the value of dn / dp. This involves a reduction, as dn / dp is always less, then 1. The difference between the model and physical reality is the greatest, when the values of force and velocity are greatest. Therefore, if two bodies get near to each other, the program is able to automatically increase accuracy by reducing the time unit. If this is the case, simulation will slow down. If the two bodies do not move off from each other, the time unit starts to increase until reaching its original value. The dynamic time unit slows down program running, even if the above condition is not met.

2.3.1.1.10  Proximity

Proximity is the number the program reckons with, if Time unit type is dynamic. It is a number of double type, cannot be zero or less.

2.3.1.1.11  Background, selection and information color

The background color is the color of the program window, and the selection color defines the color of selected bodies (see Selection) and of their names. The information color is the color of the information text, displaying in the main window. They are RGB² values. The background color and the selection color shall be easily distinguishable from each other. Background is defaulted as black, selection as white and the information is gray.

2.3.1.1.12  Repeat

It is possible to automatically restart simulation, if repeat is on and the time set in Simulation length elapses. Upon reading the program file or creating a new System or stopping the simulation automatically, body position and velocity vectors are stored in the memory for such data to be available for restart. Simulation is stopped by switching off repeat or simulation.

2.3.1.1.13  Vectors

These are the switching on/off the velocity and force vectors visibility.

2.3.1.1.14  Visible vector magnitude

Changing velocity and force vector visibility does not alter the vector itself, they appear only on the screen with a different size for the sake of better visibility. For instance, force vectors are not visible due to their small size, then by increasing this number, they are made visible. It is a number of double type, cannot be zero or less.

2.3.1.1.15  Vector color

Velocity and force vectors have colors like these, if Vectors visibility is on. They are RGB values.

2.3.1.1.16  Vectors trail

By switching on Vector trail, the last few positions of vectors become visible, if the Trail is on.

2.3.1.1.17  Trail

By switching on trail, the last few positions of bodies become visible. The maximum length of trails is defined in Trail length. Trailing is visible on the screen only temporary. If during simulation, any parameter changes, trailing starts again to provide faster operation.

2.3.1.1.18  Trail length

It defines the maximum number of Trail. If the number of trails reached this limit, then the last, oldest trail with the background color is removed from the screen. It is a number of integer³ type, cannot be zero or less, and cannot be more then 100 000.

2.3.1.1.19  Trail color type

Trail color may be defined of Body color or Trail color.

2.3.1.1.20  Trail color

This color is used to set Trail on the screen, if Trail color type is set to this color. It is an RGB value.

2.3.1.1.21  Trail size

Trail size may be the same as body diameter (see Body mass and diameter) or just a pixel.

2.3.1.1.22  Body and group name

These are switching on/off the names of Bodies and Groups. Body names are located below the bodies, and the group names are above the Mass center of the groups. Adjusting the character sets are comprehended in the section Character sets for the background and mouse pointer.

2.3.1.1.23  Body and group name color type

Body name may appear with Body color or the color as defined by Body and group name color. Group name may appear with Group color or the color as defined by body and group name color.

2.3.1.1.24  Body and group name color

Body name and Group name appears with these colors, if Body and group name color type is set to those colors. They are RGB values.

2.3.1.1.25  Mass center

By switching on the mass center, the small crosshair to illustrate the mass center for Groups becomes visible.

2.3.1.1.26  Mass center color type

The Mass center may be the Group color or the color as defined by Mass center color.

2.3.1.1.27  Mass center color

Mass center will appear with this color, if Mass center color type is set to this color.

2.3.1.1.28  Mass center trail

By switching on Mass center trail, the last few positions of mass center become visible, if the Trail is on.

2.3.1.1.29  On-Screen Information

The On-Screen Information text in the top-left corner of the main window is informed about the state of the System and the Bodies. In Edit state if the Mouse pointer is before the background, we get information about the system: view (see Change view), Zoom, time, bookmarks (see Edit bookmark) and the number of the bodies.

If the mouse pointer is before a body, we get information about the body: name (see Body name), mass and diameter (see Body mass and diameter), position and velocity vectors (see Body position and velocity vectors). If the body is selected (see Selection), holded (see Body holding) or sticked (see Stick), this information is also displayed. If the body belongs to one or more groups, we get information about the top priority group: name of the group (next to this, in brackets, the number of the groups), mass of the group, and position and velocity vector of the mass center of the group. If the body or its top proprity group is sticked, the view information displayed too. In Simulation state displayed same as in case of background, except the number of the bodies.

The color of the On-Screen Information text is the Information color (see Background, selection and information color)

2.3.1.1.30  Center of the coordinate system

By switching on Center of the coordinate system, the big cross of the origo becomes visible. The color of the Center of the coordinate system is the Information color (see Background, selection and information color)

2.3.1.1.31  Stick

You may stick a body (see Bodies) or Mass center of a group (see Groups) to the screen so that this body or mass center will be apparently stationary during the simulation. A body or mass center will be stuck is defined by Stick type and which body or mass center will be is by Body and group to stick. In Edit state, above a sticked body, the text of the Mouse pointer is underlined.

2.3.1.1.32  Stick type

An object to be stuck may be a body (see Bodies) or the Mass center of a group (see Groups).

2.3.1.1.33  Body and group to stick

They are identifiers for the body (see Bodies) and group (see Groups) to be stuck. They refer to the body and group that will stick to the screen, if Stick is switched on.

2.3.1.1.34  Warning

On switching on warning, the program will send warnings during the simulation, if the events fit to any given condition occur. Warning events define such conditions. Warnings shall appear on the screen visually or as a sound signal alone as defined by Warning type. When checking the conditions occurs is defined by Warning check time. With the warnings switched on, running rate is reduced.

2.3.1.1.35  Warning check time

Events may be checked upon computing any new position or only refreshing the screen.

2.3.1.1.36  Warning type

The type of warnings may be visual, when a message window appears on the screen or a sound signal alone. After closing the warning window, the simulation is over preventing the message to appear again on the screen. After a sound signal, the simulation goes on. The visual warning that is the message window contains the name of one or two bodies the warning was triggered by and the cause of warning.

2.3.1.1.37  Warning events

Warnings may be triggered by events as follows:

• Collision between two bodies.
• Two bodies get nearer to each other than the value defined by Warning distance.
• The speed of a body becomes higher than the value defined by Warning speed.

Two bodies are considered as collided with each other, if the distance between their centers is less than the sum of their radii.

By monitoring excessive proximity, the most inaccurate computations of modeling are filtered out, making the name of and distance between the two bodies appearing in the message window.

Filtering out any overspeed will also reduce inaccuracy, as appearing the name and speed of the body in the warning window.

2.3.1.1.38  Warning distance

When in Warning events, proximity of two bodies is on, this number gives the shortest distance just not followed by a warning. It is a number of double type, cannot be zero or less.

2.3.1.1.39  Warning speed

If in Warning events, monitoring the top speed is on, this number gives the top speed just not followed by a warning. It is a number of double type, cannot be zero or less.

2.3.1.1.40  Log

By logging, path data (position and velocity vectors) computed during simulation and possible warnings are saved in a log file in text form. The location and name of such a log file is set in the dialog window Default properties. With logging switched on, the running rate is reduced and a high volume of data may be entered in a log, whose amount depends the number of bodies and the simulation time. Compare Description of the log file.

2.3.1.1.41  Log time

Logging may occur upon computing any new position or only refreshing the screen.

2.3.1.1.42  Log type

Data of position and velocity vectors or warning or both of them may be logged.

2.3.1.1.43  System description

The system description is a description of the System in words, discussed in detail in the section System description.

1 The precision of the double type floating-point number at least 15 digits, range is ±1.7E308

2 The 3 * 8 bit RGB values are sufficient to display colors of 224 (16,777,215)

3 The 32 bit integers range from -2,147,483,648 to 2,147,483,647