externalgravity.rst

External Gravity Task Example

An example of how to implement an external gravity task in SWIFT

An external gravitational field can be imposed in SWIFT to mimic self-gravity. This is done by assigning a gravitational force that falls as $1/ r^2$ (mathjax support to be included).

In order to do this we update the files as described in :ref:`NewTask`. For the specific case of adding an external graviational field the additions are as follows:

task.h

Code (snapshot Nov 2015):

/* The different task types. */
enum task_types {
   task_type_none = 0,
   task_type_sort,
   task_type_self,
   task_type_pair,
   task_type_sub,
   task_type_ghost,
   task_type_kick1,
   task_type_kick2,
   task_type_send,
   task_type_recv,
   task_type_link,
   task_type_grav_pp,
   task_type_grav_mm,
   task_type_grav_up,
   task_type_grav_down,
   **task_type_grav_external,**
   task_type_psort,
   task_type_split_cell,
   task_type_count
};

Task of type - task_type_grav_external - added to list of tasks.

task.c

Code (snapshot Nov 2015):

/* Task type names. */
const char *taskID_names[task_type_count] = {
    "none",  "sort",    "self",    "pair",    "sub",
    "ghost", "kick1",   "kick2",   "send",    "recv",
    "link",  "grav_pp", "grav_mm", "grav_up", "grav_down", "grav_external",
    "psort", "split_cell"
 };

Task added to list of task names (used only for debugging purposed).

cell.h

Code (snapshot Nov 2015):

/* The ghost task to link density to interactions. */
   struct task *ghost, *kick1, *kick2, *grav_external;

Struture of type "task" declared (or pointer to a task at least).