The direction of the 'arrow of time', the maximum time-of-flight of a ray and time markers.
Arrow of time
Time normally runs forward in the programs, but the direction can be reversed -that is, the rays can be traced backwards in time from the initial condition.
This can be useful if you want to know where particles should start from to reach a desired final position.
This option is especially useful in CPO3D when there is a magnetic field present, because the magnetic force reverses when the velocity reverses, so that a ray cannot be retraced by starting in the normal way at the final position.
As an example of backward tracing, if you have a ray that starts at x = 0, has vx positive, and finishes at x = 1, then if backward tracing is selected and the ray is started at x = 1 with vx positive then the ray will be traced backwards to x = 0 (and note that vx is not negative, and note also that the output information for this ray will give positive vx).
This option should not be used if the rays are reflected at a mirror, because incorrect results are then sometimes obtained.
It is accessed in databuilder/tracing and screen options/ray limits.
Time limits
If you do not want to limit the time, enter a large number (for example 1.E10, or -1.E10 for a backward ray).
Again, this is accessed in databuilder/tracing and screen options/ray limits.
Time markers
This option allows small filled circles to be added to each ray at a specified time interval (which is the same for all rays). The maximum number of markers displayed for each ray is 10.
It is accessed in databuilder/tracing and screen options/advanced options.
Associated topics:
Return to general note on fields of view and ray limits.
For users who are editing or constructing an 'input data file' without the use of the data-builder -that is, pre-processor:
But Manual editing is certainly not recommended -it is a relic from the time when the databuilder was not available All users are strongly encouraged to use the databuilder, which always gives the correct formats and which has many options for which the formats are not described or easily deduced.
Enter the direction of the time as '-'.
The time marker option is triggered by an 'm' in the 12th space of the line that gives the maximum time, followed on the same line by the specified time for the marker.