Sets the evolver settings of the frontmost simulation.
When you select this command, an input dialog will be displayed showing the evolver settings of the frontmost simulation, and allowing you to modify them if desired. If you accept the input dialog, AstroGrav will change the evolver settings of the frontmost simulation to your newly specified values, and if you cancel the input dialog, AstroGrav will leave the evolver settings of the frontmost simulation unchanged. This command may be used even if the frontmost simulation is currently evolving, in which case the evolution will change immediately to using the new evolver settings if you accept the input dialog. There are the following seven settings.
Include: General Relativity allows you to choose between an evolution algorithm that uses Newton's Theory of Gravity and an evolution algorithm that uses Einstein's General Theory of Relativity. Using Newton's Theory of Gravity is faster but less accurate than using Einstein's General Theory of Relativity, and so should be chosen in situations where the effects of general relativity are unimportant. Newton's Theory of Gravity is likely to be the best choice for unstable systems, and Einstein's General Theory of Relativity is likely to be the best choice for stable systems, such as solar system simulations and exoplanet simulations.
Include: Radiation Pressure allows you to choose between an evolution algorithm that ignores radiation pressure and an evolution algorithm that takes radiation pressure into account. Ignoring radiation pressure is faster but less accurate than taking radiation pressure into account, and so should be chosen in situations where the effects of radiation pressure are unimportant. Ignoring radiation pressure is likely to be the best choice in most situations, because radiation pressure usually only has a significant effect on very small objects, such as spacecraft. The force produced by radiation pressure is dependent upon the object's mass, radius, and color, and so when studying objects such as spacecraft, it is important to get these quantities as accurate as possible. For extremely small objects such as the particles in a comet's tail, the repulsive effect of radiation pressure can exceed the attractive effect of gravity, and this results in 'anti'-hyperbolic orbits in which the object moves faster and faster as it moves away from the source of radiation. These 'anti'-hyperbolic orbits are indicated by using a negative value for the semi-major axis, instead of the usual positive value.
Time Step allows you to choose the time step you want to use when evolving. AstroGrav automatically breaks large time steps into smaller substeps as necessary to achieve an acceptable accuracy, so this setting is really the time step between consecutive displays during evolution, rather than the time step used directly for the calculations.
Threshold allows you to choose the mass threshold below which the gravitational influence of objects is ignored. The way this works is that the mutual influence of a pair of objects is ignored if and only if the sum of their masses is less than the mass threshold. This allows you to greatly speed up simulations whose objects are mostly of a low enough mass that their gravitational influence can safely be ignored. A good example is a solar system simulation containing a large number of low mass asteroids.
Collisions allows you to choose whether to ignore colliding objects (so that they pass through each other), to combine colliding objects, or to make colliding objects bounce off each other. Ignoring colliding objects is faster than combining or bouncing them because there is no need to test for collisions, so this should be the choice in situations where you know that collisions won't occur (such as a simulation of exoplanets) or in situations where collisions can safely be ignored.
Sound Effects allows you to choose whether or not to play a sound effect whenever two objects collide and combine. This may be useful if you leave a simulation running for a long time and want an audio alert whenever a collision occurs. This setting has no effect if collisions have been set to be non-combining.
Restitution allows you to choose the coefficient of restitution that is to be used during bouncing collisions. This must be a number between zero and one inclusive, with a value of zero signifying no bounce (objects just stick together), and a value of one signifying a perfect bounce. This setting has no effect on evolution if collisions have been set to be non-bouncing.
Include Friction allows you to choose whether or not to include the effect of friction during bouncing collisions. Including friction is best for simulations such as bouncing balls where the balls are required to come to rest, whereas excluding friction is best for simulations such as rotating rubble piles where conservation of angular momentum is required. This setting has no effect on evolution if collisions have been set to be non-bouncing.
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