# 20.181/Lecture6

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< 20.181

## Exams and HWs

- In-class midterm on 10/11

- studying for the exam:
- don't memorize lecture notes,
- more important to be able to work through the problems
- understand all the homeworks and you'll be prepared

### Homeworks coming up

- HW5: Due next wednesday

- downPass, maximum likelihood

- HW6:

- search tree space

## Up Pass

- If we know what the best answer is at the root- all of the other internal nodes aren't necessarily the best guess. We need an upPass algorithm that passes information from the root, back up to the leaves.

- For this example, we are dealing with
**one**column of the sequence alignment. In this simple example, we compute one possible set of internal states (but we learned that this doesn't cover all possible states - see lecture 7 for details):

def upPass(tree,parent):

- if tree is a leaf: #(stop)

- return
- i = parent <intersect> downpass
- if i = None:

- data = i <union> downpass
- upPass(left,data)
- upPass(right,data)