Carissa Black <c-black@northwestern.edu> wrote:
>> I have a few questions about Homework #1. Should we be using XOR and
>> Equivalence when optimizing? And how do you deal with don't cares in
>> QM?.. should we just ignore them like when we're doing the algebra
>> method? Also, should we answer question #8 about Espresso?

Hyerim Shin:
> for QM, you do use dont cares when you do the first stage.
> you don't use dontcares when you are doing unate covering

Hyerim Shin is right. The reason to use them in the first stage is that they
allow you to get bigger implicants. The reason not to use them in the second
stage (don't make rows for them) is that they aren't required to be covered
by any implicants in the solution. In other words, it is O.K. for the DCs to
be zeros so we shouldn't require that at least one prime covering them be
included.

-Robert Dick-
Received on Sun Oct 5 17:48:01 2008