tom's blog

Problem with 2-SAT
By tom, 10 years ago, In English

a 2-CNF formula is satisfiable if and only if there is no variable that belongs to the same strongly connected component as its negation..

Look at this example:







Any variable and its negation belong to the same strongly connected component, but it's not possible to satisfy these formulas.

What I'm doing wrong?

PS: With formula, I want to force x = 1

  • Vote: I like it
  • 0
  • Vote: I do not like it

»
10 years ago, # |
  Vote: I like it +6 Vote: I do not like it

If i remembered it correctly, for each a=>b you should also add -b=>-a edge

→ Reply
  • »
    »
    10 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    That was it. Thank you :)

    → Reply
»
10 years ago, # |
  Vote: I like it 0 Vote: I do not like it

We can derive two implications from (avb): ¬a->b, ¬b->a.

→ Reply