MTD(f) and Ghosts of Mars: Difference between pages

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{{Infobox_Film |

'''MTD(f)''', an abbreviation of MTD(n,f) (which is itself an abbreviation of Memory-enhance Test Driver with node n and value f) is a [[minimax]] search algorithm that improves on the basic [[alpha-beta pruning]] algorithm.

name = John Carpenter's Ghosts of Mars |

image =Ghostsofmars01.jpg |

imdb_id =0228333 |

writer =[[John Carpenter]]<br>Larry Sulkis |

starring =[[Ice Cube]]<br>[[Natasha Henstridge]]<br>[[Jason Statham]]<br>[[Pam Grier]]<br>[[Clea DuVall]]<br>[[Joanna Cassidy]]|

director =[[John Carpenter]] |

producer =Sandy King |

distributor =[[Storm King]] [[Screen Gems]] |

released =[[August 24]], [[2001]] ([[Theater]])<br>[[December 4]] [[2001]] ([[DVD]]) |

runtime =98 min. |

language =English |

music =[[John Carpenter]] |

awards β := g|

amg_id = 1:250566 |

budget =$28,000,000 |

}}

'''''Ghosts of Mars''''' (also known as '''''John Carpenter's Ghosts of Mars''''') is a [[2001]] movie directed by [[John Carpenter]], which in its basic themes is similar to his earlier [[Assault_on_Precinct_13_(1976_film) | Assault on Precinct 13]].

== Zero Window Searches ==

MTD(f) gets its efficiency from doing only zero-window alpha-beta searches, and using a "good" bound (variable beta) to do those zero-window searches. Conventionally AlphaBeta is called with a wide search window, as in AlphaBeta(root, -INFINITY, +INFINITY, depth), making sure that the return value lies between the value of alpha and beta. In MTD(f) a window of zero size is used, so that on each call AlphaBeta will either fail high or fail low, returning a lower bound or an upper bound on the minimax value, respectively. Zero window calls cause more cutoffs, but return less information - only a bound on the minimax value. To find the minimax value, MTD(f) has to call AlphaBeta a number of times, eventually converging towards it. The overhead of re-exploring parts of the search tree in repeated calls to AlphaBeta disappears if a [[transposition table]] is used to store and retrieve the nodes it sees in memory.

== Pseudocode Plot==

'''function''' MTDF(root, f, d)

g := f

upperBound := +∞

lowerBound := -∞

'''repeat'''

'''if''' g = lowerBound '''then'''

β := g+1

'''else'''

β := g

g := AlphaBetaWithMemory(root, β-1, β, d)

'''if''' g < β '''then'''

upperBound := g

'''else'''

lowerBound := g

'''until''' lowerBound ≥ upperBound

'''return''' g

The movie is set in the mid 22nd century. The planet [[Mars]] has been [[terraformed]], allowing Humans to walk on the surface without having to wear pressure suits. The story concerns a police officer, Melanie Ballard ([[Natasha Henstridge]]) who is leading a small team to pick up and transport a prisoner named Desolation Williams ([[Ice Cube]]). Arriving at the remote mining town where Williams is being held, Ballard finds virtually all of the people missing. On investigating she discovers that the miners found an underground doorway which had been created by an ancient [[Martian]] civilization. When the door was opened it released "ghosts", disembodied spirits who possessed the miners.

== Performance ==

Implementations of the MTD(f) algorithm had been proven to be better than other search algorithms (e.g. [[Negascout]]) in games such as chess[http://portal.acm.org/citation.cfm?id=240998&coll=GUIDE&dl=GUIDE&CFID=50049687&CFTOKEN=16181537]. However MTD(f) has practical issues in chess engines, such as the reliance on the [[transposition table]], which makes it a less desirable choice. Today most chess engine authors still prefer [[Negascout]].

Violence ensues, as the now possessed miners commit acts of [[death]] and [[destruction]], as well as [[self-mutilation]]. <!--The self mutilation however may be merely the alien spirits attempting to alter their human bodies to look more like those of the aliens themselves (which are only partially seen very briefly).-->

== External links ==

*[http://www.cs.vu.nl/~aske/mtdf.html Description of MTD(f) algorithm]

Ballard must fight off the attacking miners, escape the town, and if possible destroy the ghosts. Unfortunately all these tasks are complicated by the fact that killing a possessed human merely releases the Martian spirit, which immediately possesses another human. Eventually they decide to blow up a [[nuclear]] reactor, which kills the human hosts. All of Ballard's team are killed by the miners, leaving only her and Desolation. Not wanting the authorities to blame the massacre on him, he handcuffs Ballard to her bed and escapes the train, leaving her to return home. While she reccuperates at a hospital, the miners attack the city. Desolation returns with a pair of [[nickle]] plated [[uzi]]s and they team up to fight off the alien zombies, setting the film up for an unlikly sequel.

[[Category:Optimization algorithms]]

==Production Notes==

*Although Mars has a day/night cycle almost identical in length to Earth's, most of the movie is set at night. The only moment in which we see Mars during the daytime is in a flashback through the character of the scientist, when she talks about how she found and opened a "Pandora's Box" that let the alien spirits out.

*Much of the movie was filmed in a [[gypsum]] mine in New Mexico. The pure white gypsum had to be dyed with thousands of gallons of biodegradable red food dye to recreate the appearance of the Martian landscape.

==Trivia==

*Originally Courtney Cox was set to play Ballard but after her foot was run over accidently by her husband she was replaced by Natasha Henstridge.

*On a similar note, Jason Statham was originally set to play Desolation Williams. This film also contains Statham's first on screen kiss.

== External links ==

*{{imdb title|id=0228333|title=Ghosts of Mars}}

*[http://www.theofficialjohncarpenter.com/pages/themovies/gm/gm.html Ghosts of Mars at theofficialjohncarpenter.com]

{{John Carpenter Films}}

{{2000s-horror-film-stub}}

[[Category:2001 films]]

[[Category:Mars in fiction]]

[[Category:American films]]

[[Category:English-language films]]

[[Category:Space adventure films]]

[[Category:Films directed by John Carpenter]]

[[Category:Science fiction action films]]

[[Category:Science fiction horror films]]

[[Category:Screen Gems films]]

[[Category:Ghost films]]

[[de:Ghosts of Mars]]

[[fr:Ghosts of Mars]]

[[it:Fantasmi da Marte]]

[[ja:ゴースト・オブ・マーズ]]

[[fi:Ghosts of Mars]]