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# functions in gadget.i - C

 CHalo ``` CHalo struct CHalo { long level ; long mother; long firstchild; long nsisters; long sister; double rho_saddle; double density; double densmax; double radius ; double mass ; double position(3); // level : integer number corresponding to the level in the tree. // The root, node(1), corresponds to level=0. The root corresponds // to all the selected particles (above the density threshold) // in the simulation box: it is not physically relevant. // mother : the id of the mother of this node, i.e. the id of substructure // which contains this substructure (for the root, there is no // mother, i.e. mother=0). // firstchild : the id of the first child of this node, i.e. the first // substructure it contains. Other substructures will be found // by running over the list their sisters. If we are sitting // at the end of a branch, firstchild=0 (i.e. this node correspond // to an elementary substructure) . // nsisters : the number of sisters of this substructure + 1. // sister : the id of the sister ``at the right'' of this structure. A structure // that has not sister at its ``right'' has sister=0. // rho_saddle : the density of the saddle(s) point(s) connecting this // structure to its sisters. In principle this could be calculated // uniquely so that a structure would always have at most one // sister, but as explained in the important note above, // rho_saddle is computed approximately, as a result, it can // correspond to more than a single saddle point. // For a given density threshold, rho_th, if rho_th > rho_saddle, // the substructure is connected to its sisters, whereas if // rho_th < rho_saddle, the substructure is disconnected from its // sisters. // density : average density of the substructure, calculated from the // average SPH density of all particles with SPH density larger than // rho_saddle and belonging to the substructure. // densmax : maximum density within the substructure : it correspond // to the largest SPH density of all the particles within the // substructure. // radius : size in Mpc of the substructure calculated by computing the mean // square distance of each particle belonging to it with respect // to its center of mass. // mass : number of particles within the substructure. // position(3) : coordinates in Mpc of the center of mass of the // substructure. } ```