Description of across

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across

PURPOSE

across(g,X,Y) --- find all edges with one end in X and other end in Y.

SYNOPSIS

function elist = across(g,X,Y)

DESCRIPTION

 across(g,X,Y) --- find all edges with one end in X and other end in Y.
 We require X and Y to be disjoint. If Y is omitted, then Y = V(g)-X.
 We do not require X U Y = V(g).

CROSS-REFERENCE INFORMATION

This function calls:

• matrix matrix(g) --- return (a copy of) the adjacency matrix of g
• nv nv(g) --- number of vertices in g

This function is called by:

SOURCE CODE

0001 function elist = across(g,X,Y)
0002 % across(g,X,Y) --- find all edges with one end in X and other end in Y.
0003 % We require X and Y to be disjoint. If Y is omitted, then Y = V(g)-X.
0004 % We do not require X U Y = V(g).
0005 
0006 A = matrix(g);
0007 X = X(:);
0008 n = nv(g);
0009 
0010 if nargin==2
0011     Y = setdiff(1:n,X);
0012 end
0013 
0014 Y = Y(:);
0015 
0016 B = A(X,Y);
0017 [i,j] = find(B);
0018 
0019 ii = X(i);
0020 jj = Y(j);
0021 % make sure these are column vectors
0022 ii = ii(:);
0023 jj = jj(:);
0024 
0025 elist = [ii,jj];
0026

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