We are feeling experimental and want to create a new dish. There are various ingredients we can choose from and we’d like to use as many of them as possible, but some ingredients don’t go well with others. If there arepossible ingredients (numbered to ), we write down an matrix giving thediscordbetween any pair of ingredients. Thisdiscordis a real number between and , where means “they go together perfectly” and means “they really don’t go together.” Here’s an example matrix when there are five possible ingredients.

In this case, ingredients and go together pretty well whereasandclash badly. Notice that this matrix is necessarily symmetric; and that the diagonal entries are always . Any set of ingredients incurs apenaltywhich isthe sum of all discord values between pairs of ingredients.For instance, the set of ingredientsincurs a penalty of
.We want this penalty to be small.
EXPERIMENTAL CUISINE
Input:, the number of ingredients to choose from ;,the “ discord” matrix; some number
OUTPUT:The maximum number of ingredients we can choose with penalty .
Show that ifEXPERIMENTAL CUISINEis solvable in polynomial time, then so is 3SAT.