comparison toolboxes/FullBNT-1.0.7/graph/dfs.m @ 0:e9a9cd732c1e tip

first hg version after svn

+function [d, pre, post, cycle, f, pred] = dfs(adj_mat, start, directed)
+% DFS Perform a depth-first search of the graph starting from 'start'.
+% [d, pre, post, cycle, f, pred] = dfs(adj_mat, start, directed)
+%
+% Input:
+% adj_mat(i,j)=1 iff i is connected to j.
+% start is the root vertex of the dfs tree; if [], all nodes are searched
+% directed = 1 if the graph is directed
+%
+% Output:
+% d(i) is the time at which node i is first discovered.
+% pre is a list of the nodes in the order in which they are first encountered (opened).
+% post is a list of the nodes in the order in which they are last encountered (closed).
+% 'cycle' is true iff a (directed) cycle is found.
+% f(i) is the time at which node i is finished.
+% pred(i) is the predecessor of i in the dfs tree.
+%
+% If the graph is a tree, preorder is parents before children,
+% and postorder is children before parents.
+% For a DAG, topological order = reverse(postorder).
+%
+% See Cormen, Leiserson and Rivest, "An intro. to algorithms" 1994, p478.
+
+n = length(adj_mat);
+
+global white gray black color
+white = 0; gray = 1; black = 2;
+color = white*ones(1,n);
+
+global time_stamp
+time_stamp = 0;
+
+global d f
+d = zeros(1,n);
+f = zeros(1,n);
+
+global pred
+pred = zeros(1,n);
+
+global cycle
+cycle = 0;
+
+global pre post
+pre = [];
+post = [];
+
+if ~isempty(start)
+  dfs_visit(start, adj_mat, directed);
+end
+for u=1:n
+  if color(u)==white
+    dfs_visit(u, adj_mat, directed);
+  end
+end
+
+
+%%%%%%%%%%
+
+function dfs_visit(u, adj_mat, directed)
+
+global white gray black color time_stamp d f pred cycle  pre post
+
+pre = [pre u];
+color(u) = gray;
+time_stamp = time_stamp + 1;
+d(u) = time_stamp;
+if directed
+  ns = children(adj_mat, u);
+else
+  ns = neighbors(adj_mat, u);
+  ns = setdiff(ns, pred(u)); % don't go back to visit the guy who called you!
+end
+for v=ns(:)'
+  %fprintf('u=%d, v=%d, color(v)=%d\n', u, v, color(v))
+  switch color(v)
+    case white, % not visited v before (tree edge)
+     pred(v)=u;
+     dfs_visit(v, adj_mat, directed);
+   case gray, % back edge - v has been visited, but is still open
+    cycle = 1;
+    %fprintf('cycle: back edge from v=%d to u=%d\n', v, u);
+   case black, % v has been visited, but is closed
+    % no-op
+  end
+end
+color(u) = black;
+post = [post u];
+time_stamp = time_stamp + 1;
+f(u) = time_stamp;
+
+