Inductive Programming

Lloyd Allison, School of Computer Science & Software Engineering, Monash University, Clayton, Victoria, Australia 3800.
To: AIG, Dept. Comp. Sci., University of York, 12.15, Monday 11 October 2004.

Seminar's area: Inductive inference,   i.e. inferring general models from given data  (artificial intelligence, data mining, machine learning).

Research problem: What are statistical models?

I.e. What do they do?  What can be done to them?  How can you combine two or more of them?  And what do you get?  How can you program with them?   What are the operations, types, classes, semantics?

This talk describes an approach and gives practical examples.

www.csse.monash.edu.au/~lloyd/Seminars/200410-II/index.shtml  

Motivation 1

Given a new problem in general computing,
the probability of having an existing solution is ~0, ...
programming languages (e.g. Haskell) exist to ease writing new solutions.

Given a new inductive inference problem,
the probability of having an existing solution is ~0, ...
<?what?> exists to ease writing new solutions?

Motivation 2

repeat {
    new postgrad starts in machine learning;
    devises new model   (or variation);
    does some maths   (not just a hacker);
    implements search & estimators   (practical too!);
    does comparative tests v. other methods   (beats them);
    writes thesis, gets degree & leaves.
}

We are often left with programs that are hard to (re-) use -- undocumented code, not robust, different I/O formats, reinvented wheels, etc..  Can this be better organised?

1. A Toy Example

@0 -- continuous
@1 -- Boolean
@2 -- Boolean
@3 -- Boolean
@4 -- continuous.

Bayesian networks can "learn & explain" relationships between attributes (variables).

N. Friedman and M. Goldszmidt.   Learning Bayesian networks with local structure.   UAI'96, pp.252--262, 1996,

suggested using classification trees in the nodes of a Bayesian network.

Oh good, we just happen [1] to have:

estCTree ::  ([opSpace] -> Model opSpace)  -> [ipSpace] -> [opSpace]  -> CTreeType ipSpace opSpace







(Taking small liberties with the types.-)

the toy e.g. (5 attributes)

general mixed Bayesian network

An Inferred Bayesian Network

details of the network's nodes next...


{CTleaf N(1.0,0.41)(+-0.1),_,_,_,_}, --@0

{CTleaf _,mState[0.5,0.5],_,_,_},   --@1

{CTfork @0<|>=1.4[                  --@2|@0,@1
  {CTleaf _,_,mState[0.99,0.01],_,_},
  {CTfork @1=False|True[
    {CTleaf _,_,mState[0.98,0.02],_,_},
    {CTleaf _,_,mState[0.02,0.98],_,_}]}]}, 

{CTleaf _,_,_,mState[0.5,0.5],_},   --@3

{CTfork @2=False|True[              --@4|@0,@2
  {CTfork @0<|>=1.0[
    {CTleaf _,_,_,_,N(0.55,0.2)(+-0.1)},
    {CTfork @0<|>=1.4[
      {CTleaf _,_,_,_,N(1.0,0.2)(+-0.1)},
      {CTleaf _,_,_,_,N(1.45,0.2)(+-0.1)}]}]},
  {CTleaf _,_,_,_,N(3.45,0.2)(+-0.1)}]}

N.B. Don't get the nodes of the network and of a tree confused!

Components

mState[p0,p1,...] -- multi-state distribution[*].

N(m,s) -- normal (Gaussian) distribution[*].

"classification" tree[*],

    CTleaf -- model[*] an attribute,

    CTfork -- test[*] an attribute.

 

([*] message lengths, i.e. complexities, direct search & prevent over-fitting.)

2. A Real Example: Lost Person

data Tipe = Alzheimers | Child | Despondent | Hiker | ...

type Age = Double

data Race = White | Black deriving (Eq, Enum,...

data Gender = Male | Female deriving (Eq, Enum,...

data Topography = Mountains | Piedmont | Tidewater deriving...

data Urban = Rural | Suburban | Urban deriving (Eq,Ord,...

type HrsNt = Double -- hours notified

type DistIPP = Double -- distance
...

(See Koester, and also Twardy & Hope.)

Estimators

type MissingPerson = (Maybe Tipe, Maybe Age, ...)

e0 = (estModelMaybe estMultiState)   --Tipe

e1 = (estModelMaybe (estNormal 0 90 1 70 0.5))   --Age

...

e7 = (estModelMaybe (estNormal 0 50 0.5 30 0.2)) --DistIPP

estimator = estVariate15 e0 e1 e2 e3 e4 e5 e6 e7 e8 e9 e10 e11 e12 e13 e14

NB. There is(n't:-) a lot of missing data.

mixed general Bayesian network

1st Inferred Network for 8 attributes

Inferred Network's Trees...

Net:[
 -- @1, Age:
 {CTleaf _,(Maybe 50:50,N(40.6,27.5)... },

 ... etc. ...

 -- @6, HrsNt:
 {CTfork @1(<|>=62.0|?)[
  {CTleaf...,(Maybe 50:50,N( 8.7, 7.6)...},
  {CTleaf...,(Maybe 50:50,N(21.4,26.3))...},
  {CTleaf...,(Maybe 50:50,N(20.0,..1-case)..}
]},

... ]

network: 115.1 nits + data: 5396.6 nits
null:   5935.6 nits (@0..@7)

E.g. A High-Order Function of an Estimator

estModelMaybe estModel dataSet =
 let
  present (Just _) = True
  present Nothing  = False
  m1 = uniformModelOfBool          -- [*]
  m2 = estModel (map (\(Just x) -> x)
                (filter present dataSet))
 in modelMaybe m1 m2

[*] or if modelling missing-ness...
    m1 = estMultiState (map present dataSet)

Classes e.g.

class Project t where   -- as in `projection'
 select :: [Bool] -> t -> t
 selAll :: t -> [Bool]  -- all True flags

A type, t, in class Project can be projected onto a select-ed sub-space.
E.g. A 15-dim'n estimator, such as estVariate15 e0...e14.

Also a related class for select-ive partitioning of data within trees.

print warning: May lose network's lines if shrunk.
 
e.g.   mixed general Bayesian network

 
@0:Tipe = Alzheimers | Child |...
@1:Age  
@2:Race = ...| ...
@3:Gender = ...| ...
@4:Topography = ...| ...| ...
@5:Urban = ...| ...| ...
@6:HrsNt  
@7:DistIPP  
@8:TrackOffset  
@9:Health = Well | Hurt | Dead --after!  
@10:Outcome = Find | Suspended | Invalid
@11:FindRes = Ground | Air |...| Dog
@12:FindLoc = Brush | Woods |...
@13:HrsFind  
@14:HrsTot  
A Network Inferred for all 15 Attributes of `lost persons'

Summary

Have types and type-classes for Models, Function-Models and Time-Series models. Polymorphic types, type classes, high-order functions, lazy-evaluation -- all useful.

Easy to write a new model, e.g. ModelMaybe & Bayesian network, to suit a new problem.

Other case studies include -- mixture models (clustering), time-series, Markov models, mixtures of Markov models, function models (regressions), etc..

[1] L. Allison. Types and classes of machine learning and data mining. 26th Australasian Computer Science Conference (ACSC), Adelaide, pp.207--215, Feb. 2003.
L. Allison. Inductive inference 1. TR 2003/148, Dec. 2003, and also Inductive inference 1.1. TR 2004/153, May 2004, School of Comp. Sci. & Software Eng., Monash University.
L. Allison. Models for machine learning and data mining in functional programming. J. Functional Prog. 15(1) pp.15-32 Jan 2005 (online 23/7/2004).
R. J. Koester. Virginia dataset on lost-person behaviour. Author's site http://www.dbs-sar.com/, 2001.
S. Peyton-Jones & others. Report on the Programming Language Haskell-98. Available at http://www.haskell.org/, 1999.
C. R. Twardy. SARbayes: Predicting lost person behavior. Presented to National Association of Search and Rescue (NASAR), Charlotte, 2002.
C. R. Twardy & L. Hope. Missing data on missing persons. submitted 2004.

© L. Allison, School of Computer Science and Software Engineering, Monash University, Australia 3800.
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