# Are we supposed to memorize Karnaugh maps?

1. Jan 25, 2012

### tamtam402

Hey guys, my professor briefly introduced Karnaugh maps and I was wondering if I'm supposed to memorize which areas correspond to which inputs (bits). Is there a trick to rebuild Karnaugh maps from memory? Just to be clear, I know how to use them to find a minimal sum of products, I'm talking about the maps "frames".

2. Jan 25, 2012

### Antiphon

No. Each map is unique to the problem at hand. Memorize the reductions.

3. Jan 25, 2012

### tamtam402

I'm not talking about the filled map, I'm talking about the "shell". For example, a 3 inputs map can always be drawn this way:

0 Y XY X
Z YZ XYZ XZ

Then, if I were asked to write an expression for F = ƩX,Y,Z(0,2,7), the filled map would look like this:

0 = 000, 2 = 010 and 7 = 111. Which means:

1 1 0 0
0 0 1 0

EDIT: you were referencing to the 2nd part of the problem. I know the filled map is unique. I'm asking about the shell of the map, which will always have the same possible forms for a X inputs. Obviously the possible forms are easy to find for a 3 input map, but you should understand what I'm talking about.

4. Jan 26, 2012

### DragonPetter

I think you should memorize the order of the bits for 2, 3, and 4 variable karnaugh maps . . its just remembering that one of the bit orders is flipped with 3 and 4 variables. That way you can set up your maps for those cases. This will cover you in an exam, but the professor might even be nice and write out the empty map for you. But you don't need to memorize this later in life if that's what you're asking.

5. Jan 26, 2012

### phinds

It is utterly irrelevant what order you use to lay out the variables in a K-map. As long as you are consistent between what you draw and how you interpret it, you'll get the exact same answer regardless of the order of the variables.

If your prof wants you to stick to some specific layout, he is being WAY overly anal about it.

6. Jan 26, 2012

### psparky

As you come along in your studies....solving the maps will be the easy part.

Setting up the maps from a tricky circuit will be the bigger challenge eventually.