Difference between revisions of "Exact real arithmetic"
(The Most Unreliable Technique in the World to compute pi) 
(Theory itemized) 

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== Theory == 
== Theory == 

⚫  Jean Vuillemin's [http://www.inria.fr/rrrt/rr0760.html Exact real computer arithmetic with continued fractions] is very good article on the topic itself. It can serve also as a good introductory article, too, because it presents the connections to both mathematical analysis and [[Computer science#Computability theoryComputability theory]]. It discusses several methods, and it describes some of them in more details. 

−  [http://www.cs.bham.ac.uk/~mhe/ Martín Escardó]'s project [http://www.dcs.ed.ac.uk/home/mhe/plume/ A Calculator for Exact Real Number Computation]  its chosen functional language is Haskell, mainly because of its purity, lazyness, presence of lazy lists, pattern matching. 

⚫  * Jean Vuillemin's [http://www.inria.fr/rrrt/rr0760.html Exact real computer arithmetic with continued fractions] is very good article on the topic itself. It can serve also as a good introductory article, too, because it presents the connections to both mathematical analysis and [[Computer science#Computability theoryComputability theory]]. It discusses several methods, and it describes some of them in more details. 

−  Martín Escardó has many exact real arithetic materials also among his many [http://www.cs.bham.ac.uk/~mhe/papers/index.html papers]. 
+  * [http://www.cs.bham.ac.uk/~mhe/ Martín Escardó]'s project [http://www.dcs.ed.ac.uk/home/mhe/plume/ A Calculator for Exact Real Number Computation]  its chosen functional language is Haskell, mainly because of its purity, lazyness, presence of lazy lists, pattern matching. Martín Escardó has many exact real arithetic materials also among his many [http://www.cs.bham.ac.uk/~mhe/papers/index.html papers]. 
−  +  * [http://users.info.unicaen.fr/~karczma/arpap/ Jerzy Karczmarczuk]'s paper with the funny title [http://users.info.unicaen.fr/~karczma/arpap/lazypi.ps.gz The Most Unreliable Technique in the World to compute pi] describes how to compute Pi as a lazy list of digits. 

== Portallike homepages == 
== Portallike homepages == 
Revision as of 14:14, 20 October 2006
Contents
Introduction
Exact real arithmetic is an interesting area: it is a deep connection between
 numeric methods
 and deep theoretic fondations of algorithms (and mathematics).
Its topic: computable real numbers raise a lot of interesting questions rooted in mathematical analysis, arithmetic, but also Computability theory (see numbersasprograms approaches).
Computable reals can be achieved by many approaches  it is not one single theory.
What it is not
Exact real arithmetic is not the same as fixed arbitrary precision reals (see Precision(n)
of Yacas).
Exact reals must allow us to run a huge series of computations, prescribing only the precision of the end result. Intermediate computations, and determining their necessary precision must be achieved automatically, dynamically.
Maybe another problem, but it was that lead me to think on exact real arithmetic: using some Mandelbrotplotting programs, the number of iterations must be prescribed by the user at the beginning. And when we zoom too deep into these Mandelbrot worlds, it will become ragged or smooth. Maybe solving this particular problem does not need necessarily the concept of exact real arithmetic, but it was the first time I began to think on such problems.
See other numeric algorithms at Libraries and tools/Mathematics.
Why, are there reals at all, which are defined exactly, but are not computable?
See e.g. Chaitin's construction.
Theory
 Jean Vuillemin's Exact real computer arithmetic with continued fractions is very good article on the topic itself. It can serve also as a good introductory article, too, because it presents the connections to both mathematical analysis and Computability theory. It discusses several methods, and it describes some of them in more details.
 Martín Escardó's project A Calculator for Exact Real Number Computation  its chosen functional language is Haskell, mainly because of its purity, lazyness, presence of lazy lists, pattern matching. Martín Escardó has many exact real arithetic materials also among his many papers.
 Jerzy Karczmarczuk's paper with the funny title The Most Unreliable Technique in the World to compute pi describes how to compute Pi as a lazy list of digits.
Portallike homepages
Exact Computation
There are functional programming materials too, even with downloadable Haskell source.
ExactRealArithmetic
This HaWiki article provides links to many implementations.