nbodykit.algorithms.fibercollisions

Classes

FiberCollisions(ra, dec[, collision_radius, …]) Run an angular FOF algorithm to determine fiber collision groups from an input catalog, and then assign fibers such that the maximum amount of object receive a fiber.
class nbodykit.algorithms.fibercollisions.FiberCollisions(ra, dec, collision_radius=0.017222222222222226, seed=None, degrees=True, comm=None)[source]

Run an angular FOF algorithm to determine fiber collision groups from an input catalog, and then assign fibers such that the maximum amount of object receive a fiber.

This amounts to determining the following population of objects:

  • population 1:
    the maximal “clean” sample of objects in which each object is not angularly collided with any other object in this subsample
  • population 2:
    the potentially-collided objects; these objects are those that are fiber collided + those that have been “resolved” due to multiple coverage in tile overlap regions

Results are computed when the object is inititalized. See the documenation of run() for the attributes storing the results.

Parameters:
  • ra (array_like) – the right ascension coordinate column
  • dec (array_like) – the declination coordinate column
  • collision_radius (float, optional) – the size of the angular collision radius (in degrees); default is 62 arcseconds
  • seed (int, optional) – the random seed to use when determining which objects get fibers
  • degrees (bool, optional) – set to True if the units of ra and dec are degrees

References

Methods

run() Run the fiber assignment algorithm.
run()[source]

Run the fiber assignment algorithm. This attaches the following attribute to the object:

Note

The labels attribute has a 1-to-1 correspondence with the rows in the input source.

labels

a CatalogSource that has the following columns:

  • Label :
    the group labels for each object in the input CatalogSource; label == 0 objects are not in a group
  • Collided :
    a flag array specifying which objects are collided, i.e., do not receive a fiber
  • NeighborID :
    for those objects that are collided, this gives the (global) index of the nearest neighbor on the sky (0-indexed) in the input catalog source, else it is set to -1
Type:ArrayCatalog; size: size