spambgon + unix email the spambgon design allows integration with standard unix mail handling unix...

SpamBGon + Unix email

The SpamBGon design allows integration with standard UNIX mail handling

UNIX mail processing looks like this: Remote sender -> local mail daemon

(MTA; e.g. sendmail or exim) MTA looks for ~/.forward file MTA pipes mail through .forward .forward decides what to do with mail Can call filter program procmail

from .forward

Putting the parts together Tell .forward to filter your mail through

the procmail program:|/usr/bin/procmail -f-

Set up a .procmailrc file with the following rules:# PATH must include javaPATH=/bin:/usr/bin:/usr/local/binMAILDIR=$HOME/mymaildir:0fw|java BSFTest -k stuff ...

:0:* ^X-Spam-Status: SPAMmy-spam-folder

For More Info...

man procmail man procmailrc man exim man spamassassin

A*

The Basic Setup, Reprise

Puzzle game: set of states+moves Apply a move/action to a state to

generate a next state Group of all states reachable in some

single move from state s are the children/ successors of s

Whole thing forms a directed graph; possibly acyclic, but more usually possessing cycles

Every move associated with a cost: c(s,a,s’)=cost to go from s to s’ via a

Object: find min cost path from start to goal

Some Terminology

Start

Goal

Some Terminology

Start

GoalStates that have been visited; had all childrengenerated == “closed”

Some Terminology

Start

GoalStates that have been generated, but notexamined; children not generated == “open”

Some Terminology

Start

Goal“Open” set forms a “fringe” or “frontier”around closed set.

Some Terminology

Start

GoalGenerating children for s moves it from opento closed and expands frontier. Adds its children to open.

s

Some Terminology

Start

Goal

s

Length of shortest path from start to s: g(s)

Some Terminology

Start

Goal

s

Length of shortest path from start to s: g(s)

Note! May bemultiple paths to s --not guaranteed thatfirst path to s isshortest path to it!

Some Terminology

Start

Goal

s

Estimated shortest dist froms to goal == h(s)(this is the heuristic function)

h(s)

Some Terminology

Start

Goal

s

g(s)+h(s)=f(s)Estimated total cost fromstart to goal

h(s)

Search Strategies

Closed list (set) things can be ignored Hard problem: which open list (set) thing

do we examine next? Strategies:

Smallest h(s)

Search Strategies

Closed list (set) things can be ignored Hard problem: which open list (set) thing

do we examine next? Strategies:

Smallest h(s) -- “greedy” search

Search Strategies

Closed list (set) things can be ignored Hard problem: which open list (set) thing

do we examine next? Strategies:

Smallest h(s) -- “greedy” search Smallest g(s)

Search Strategies

Closed list (set) things can be ignored Hard problem: which open list (set) thing

do we examine next? Strategies:

Smallest h(s) -- “greedy” search Smallest g(s) -- Breadth-first search

(BFS)

Search Strategies

CLOSED list (set) things can be ignored Hard problem: which OPEN list (set) thing

do we examine next? Strategies:

Smallest h(s) -- “greedy” search Smallest g(s) -- Breadth-first search

(BFS) Ignore h() and g(); just take things off

OPEN in LIFO order

Search Strategies

CLOSED list (set) things can be ignored Hard problem: which OPEN list (set) thing

do we examine next? Strategies:

Smallest h(s) -- “greedy” search Smallest g(s) -- Breadth-first search

(BFS) Ignore h() and g(); just take things off

OPEN in LIFO order -- Depth-first search (DFS)

Search Strategies

CLOSED list (set) things can be ignored Hard problem: which OPEN list (set) thing

do we examine next? Strategies:

Smallest h(s) -- “greedy” search Smallest g(s) -- Breadth-first search (BFS) Ignore h() and g(); just take things off

OPEN in LIFO order -- Depth-first search (DFS)

Smallest f(s) -- “Algorithm A”

From “A” to “A*” Unless we add additional conditions,

Algorithm A is not guaranteed to do any better than anything else

Recall roll of h(s) -- the heuristic Estimate of smallest cost from s to goal

We will restrict h(s) to be admissible Defn: Let h*(s) be the true min cost to

goal Defn: Heuristic h(s) is admissible iff

h(s)≤h*(s) s An admissible heuristic is an underestimate

of how hard it is to get to the goal -- optimistic

Algorithm A + admissible h() -> A*

From A* to Dijkstra’s A* guarantees:

When the goal is first opened, we will have the shortest path to the goal

I.e., as soon as you find the goal, you can stop and know you have the optimal path

Does not guarantee that you have the shortest path to any other node

Need additional constraint on heuristic Defn: Iff h(s)≤c(s,a,s’)+h(s’) then h(s) is

monotonic (a.k.a., consistent) A* + monotonic heuristic Dijkstra’s alg Guarantees that first path to any node is

shortest

Exercise

For the 15-puzzle (4^2-1) c(s,a,s’)=1 a, s s’ Examine the following heuristics: are they

admissible? Monotonic? Are they equivalent to other things you’ve seen? h(s)=0 s h(s)=37.2 s h(s)= s h(s)=“# tiles out of place” s

Can you construct an admissible, but non-monotonic heuristic?

Keeping Track...

Problem: if h() is not monotonic, can’t guarantee that you’re truly finished with anything on CLOSED

Might be able to find something a second time by a shorter path

Keeping Track...

Start

Goal

Keeping Track...

Start

Goal

s

Keeping Track...

Start

Goal

s

Keeping Track...

Start

Goal

s

Keeping Track...

Problem: if h() is not monotonic, can’t guarantee that you’re truly finished with anything on CLOSED

Might be able to find something a second time by a shorter path

Could have better path to something on CLOSED or on OPEN

Have to update that node with new “best path” to it Also have to handle all children!

How?

The Algorithm, Piece by Piece

CLOSED={}; OPEN={ START }

The Algorithm, Piece by Piece CLOSED={}; OPEN={ START } while (!OPEN.isEmpty())

s=OPEN.getFirst();

The Algorithm, Piece by Piece CLOSED={}; OPEN={ START } while (!OPEN.isEmpty())

s=OPEN.getFirst(); if (s.goalP()) { return path-to-s; }

The Algorithm, Piece by Piece CLOSED={}; OPEN={ START } while (!OPEN.isEmpty())

s=OPEN.getFirst(); if (s.goalP()) { return path-to-s; } cIter=s.children();

The Algorithm, Piece by Piece CLOSED={}; OPEN={ START } while (!OPEN.isEmpty())

s=OPEN.getFirst(); if (s.goalP()) { return path-to-s; } cIter=s.children(); while (cIter.hasNext())

The Algorithm, Piece by Piece CLOSED={}; OPEN={ START } while (!OPEN.isEmpty())

s=OPEN.getFirst(); if (s.goalP()) { return path-to-s; } cIter=s.children(); while (cIter.hasNext())

child=cIter.next();

The Algorithm, Piece by Piece CLOSED={}; OPEN={ START } while (!OPEN.isEmpty())

s=OPEN.getFirst(); if (s.goalP()) { return path-to-s; } cIter=s.children(); while (cIter.hasNext())

child=cIter.next(); if (CLOSED.contains(child)) {

if (child.heuristic() < CLOSED.get(child).heuristic())

The Algorithm, Piece by Piece CLOSED={}; OPEN={ START } while (!OPEN.isEmpty())

s=OPEN.getFirst(); if (s.goalP()) { return path-to-s; } cIter=s.children(); while (cIter.hasNext())

child=cIter.next(); if (CLOSED.contains(child)) {

if (child.heuristic() < CLOSED.get(child).heuristic()) {

// remove child from CLOSED; // insert child into OPEN; // discard version from CLOSED. // Why?

}

The Algorithm, Piece by Piece CLOSED={}; OPEN={ START } while (!OPEN.isEmpty())

s=OPEN.getFirst(); if (s.goalP()) { return path-to-s; } cIter=s.children(); while (cIter.hasNext())

child=cIter.next(); if (CLOSED.contains(child)) {

if (child.heuristic() < CLOSED.get(child).heuristic()) {

// remove child from CLOSED; // insert child into OPEN; // discard version from CLOSED. // Why?

} else { // discard child and cont }

}

The Algorithm, Piece by Piece else if (OPEN.contains(child))

if (child.heuristic() <

OPEN.get(child).heuristic()) {

The Algorithm, Piece by Piece else if (OPEN.contains(child))

if (child.heuristic() <

OPEN.get(child).heuristic()) { // remove prev version of child from // OPEN and insert new child }

The Algorithm, Piece by Piece else if (OPEN.contains(child))

if (child.heuristic() <

OPEN.get(child).heuristic()) { // remove prev version of child from // OPEN and insert new child } else { // discard child and continue }

}

The Algorithm, Piece by Piece else if (OPEN.contains(child))

if (child.heuristic() <

OPEN.get(child).heuristic()) { // remove prev version of child from // OPEN and insert new child } else { // discard child and continue }

} else { // child not on OPEN or CLOSED OPEN.insert(child); }

The Algorithm, Piece by Piece else if (OPEN.contains(child))

if (child.heuristic() <

OPEN.get(child).heuristic()) { // remove prev version of child from // OPEN and insert new child } else { // discard child and continue }

} else { // child not on OPEN or CLOSED OPEN.insert(child); }

CLOSED.insert(s);