Algorithm : 	a simple heuristic algorithm for minimum coloring
		(ALGORITHM 2.4.6 in Micheli Book (page 62) )
		1) sort vertex by degree of vertex. (use qsort() in stdlib.h )
			( I think that graph coloring after sorting by degree is better than random sequence graph coloring in textboot in many cases. )
		2) graph coloring.
Environment : UNIX Solaris SunOS 5.7
Target : simple graph
FILE :
	graph.c, graph.h : vertex and edge structure and access function
	hw1.c	: algorithm main program
	gen_matrix.c : matrix generation program
Usage : 
	make gen : make execution program, gen_matrix. This generates the input matrix at input.txt file
	make hw1 : make execution program, hw1. This reads the input.txt and prints color of each vertex and maximum color number