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+kruskal(1) -- Find the minimum/maximum spanning tree of a graph
+======
+
+## SYNOPSIS
+
+`kruskal` <graph_in> [MAX]
+
+## DESCRIPTION
+
+`kruskal` computes the minimum (or maximum) spanning tree of
+<graph_in>, using the Kruskal's algorithm. If <grahp_in> is
+unweighted, `kruskal` computes one of the spanning trees of the
+graph. The program prints on output the (weighted) edge list of the
+spanning tree.
+
+## PARAMETERS
+
+* <graph_in>:
+    undirected input graph (edge list). It must be an existing file.
+    
+* `MAX`:
+    If the second (optional) parameter is equal to `MAX`, compute the
+    maximum spanning tree. Otherwise, compute the minimum spanning tree.
+
+## OUTPUT
+
+The program prints on STDOUT the edge list of the minimum (maximum)
+spannig tree of <graph_in>, in the format:
+
+        i_1 j_1 w_ij_1
+        i_2 j_2 w_ij_2
+        ....
+
+
+## EXAMPLES
+
+To find the minimum spanning tree of the graph `stocks_62_weight.net`
+(the network of stocks in the New York Exchange market) we use the
+command:
+
+        $ kruskal stocks_62_weight.net
+        52 53 0.72577357
+        43 53 0.72838212
+        2 53 0.72907212
+        ...
+        36 53 0.7973488
+        53 58 0.79931683
+        26 27 0.8029602
+        $
+        
+which prints on output the edge list of the minimum spanning tree.
+However, since the weight of each edge in that graph indicates the
+similarity in the behaviour of two stocks, the maximum spanning tree
+contains information about the backbone of similarities among
+stocks. To obtain the maximum spannin tree, we just specify `MAX` as
+second parameter:
+
+        $ kruskal stocks_62_weight.net MAX
+        56 58 1.523483
+        2 52 1.3826744
+        32 51 1.3812241
+        ...
+        33 55 0.86880272
+        7 28 0.8631584
+        1 53 0.81876166
+        $
+
+## SEE ALSO
+
+clust_w(1), dijkstra(1), largest_component(1)
+
+## REFERENCES
+
+
+* J\. B. Kruskal. "On the shortest spanning subtree of a graph and the
+  traveling sales-man problem". P. Am. Math. Soc. 7 (1956),
+  48-48.
+
+* V\. Latora, V. Nicosia, G. Russo, "Complex Networks: Principles,
+  Methods and Applications", Appendix 20, Cambridge University Press
+  (2017)
+
+* V\. Latora, V. Nicosia, G. Russo, "Complex Networks: Principles,
+  Methods and Applications", Chapter 10, Cambridge University Press
+  (2017)
+
+## AUTHORS
+
+(c) Vincenzo 'KatolaZ' Nicosia 2009-2017 `<v.nicosia@qmul.ac.uk>`.