  This paper investigates an extremely classic NP-complete problem: How to
determine if a graph G, where each vertex has a degree of at most 4, can be
3-colorable(The research in this paper focuses on graphs G that satisfy the
condition where the degree of each vertex does not exceed 4. To conserve space,
it is assumed throughout the paper that graph G meets this condition by
default.). The author has meticulously observed the relationship between the
coloring problem and semidefinite programming, and has creatively constructed
the corresponding semidefinite programming problem R(G) for a given graph G.
The construction method of R(G) refers to Theorem 1.1 in the paper. I have
obtained and proven the conclusion: A graph G is 3-colorable if and only if the
objective function of its corresponding optimization problem R(G) is bounded,
and when the objective function is bounded, its minimum value is 0.
