geodist                 package:sna                 R Documentation

_F_u_n_d _t_h_e _N_u_m_b_e_r_s _a_n_d _L_e_n_g_t_h_s _o_f _G_e_o_d_e_s_i_c_s _A_m_o_n_g _N_o_d_e_s _i_n _a _G_r_a_p_h

_D_e_s_c_r_i_p_t_i_o_n:

     'geodist' uses a BFS to find the number and lengths of geodesics
     between all nodes of 'dat'.  Where geodesics do not exist, the
     value in 'inf.replace' is substituted for the distance in
     question.

_U_s_a_g_e:

     geodist(dat, inf.replace=Inf)

_A_r_g_u_m_e_n_t_s:

     dat: one or more input graphs. 

inf.replace: the value to use for geodesic distances between
          disconnected nodes; by default, this is equal 'Inf'. 

_D_e_t_a_i_l_s:

     This routine is used by a variety of other functions; many of
     these will allow the user to provide manually precomputed
     'geodist' output so as to prevent expensive recomputation.  Note
     that the choice of one greater than the maximum path length for
     disconnected vertex pairs is non-canonical (albeit common), and
     some may prefer to simply treat these as missing values. 
     'geodist' (without loss of generality) treats all paths as
     directed, a fact which should be kept in mind when interpreting
     'geodist' output.

_V_a_l_u_e:

     A list containing:

  counts: A matrix containing the number of geodesics between each pair
          of vertices

   sigma: A matrix containing the geodesic distances between each pair
          of vertices

_N_o_t_e:

     Before 'sna' version 0.5, 'inf.replace' defaulted to 'NROW(dat)'.

_A_u_t_h_o_r(_s):

     Carter T. Butts buttsc@uci.edu

_R_e_f_e_r_e_n_c_e_s:

     Brandes, U.  (2000).  ``Faster Evaluation of Shortest-Path Based
     Centrality Indices.'' _Konstanzer Schriften in Mathematik und
     Informatik_, 120.

     West, D.B.  (1996).  _Introduction to Graph Theory._  Upper Saddle
     River, N.J.: Prentice Hall.

_S_e_e _A_l_s_o:

     'component.dist', 'components'

_E_x_a_m_p_l_e_s:

     #Find geodesics on a random graph
     gd<-geodist(rgraph(15))

     #Examine the number of geodesics
     gd$counts

     #Examine the geodesic distances
     gd$gdist

