Difference between revisions of "Exact real arithmetic"
(The Most Unreliable Technique in the World to compute pi) 
(→Theory: about the paper  it's very good! read it!) 

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== Introduction == 
== Introduction == 

−  Exact real arithmetic is an interesting area: it is a deep connection between 
+  Exact real arithmetic is an interesting area: it is based on a deep connection between 
* numeric methods 
* numeric methods 

−  * and deep theoretic 
+  * and deep theoretic foundations of algorithms (and mathematics). 
Its topic: computable real numbers raise a lot of interesting questions rooted in mathematical analysis, arithmetic, but also [[Computer science#Computability theoryComputability theory]] (see numbersasprograms approaches). 
Its topic: computable real numbers raise a lot of interesting questions rooted in mathematical analysis, arithmetic, but also [[Computer science#Computability theoryComputability theory]] (see numbersasprograms approaches). 

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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. 
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 
+  Maybe another problem, but it was that lead me to think about 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 
+  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 necessarily need the concept of exact real arithmetic, but it was the first time I began to think about such problems. 
See other numeric algorithms at [[Libraries and tools/Mathematics]]. 
See other numeric algorithms at [[Libraries and tools/Mathematics]]. 

−  === Why 
+  === Why are there reals at all which are defined exactly, but are not computable? === 
See e.g. [[Chaitin's construction]]. 
See e.g. [[Chaitin's construction]]. 

== 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 

−  [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 also serve as a good introductory article, 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 ''(wonderful, wonderful! gem of a)'' 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. 

+  
+  == Implementations == 

+  
+  See [[Libraries and tools/Mathematics]] 

−  The serious 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] by Jerzy Karczmarczuk describes how to compute Pi as a lazy list of digits. 

== Portallike homepages == 
== Portallike homepages == 

−  +  * [http://wwwhomes.doc.ic.ac.uk/~ae/exactcomputation/ Exact Computation]: There are functional programming materials too, even with downloadable Haskell source. 

−  There are functional programming materials too, even with downloadable Haskell source. 

−  === [http://www.haskell.org/hawiki/ExactRealArithmetic ExactRealArithmetic] === 

−  This HaWiki article provides links to many implementations. 

+  [[Category:Mathematics]] 

[[Category:theoretical foundations]] 
[[Category:theoretical foundations]] 
Latest revision as of 19:45, 26 December 2012
Contents
Introduction
Exact real arithmetic is an interesting area: it is based on a deep connection between
 numeric methods
 and deep theoretic foundations 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 about 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 necessarily need the concept of exact real arithmetic, but it was the first time I began to think about 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 also serve as a good introductory article, 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 (wonderful, wonderful! gem of a) 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.
Implementations
See Libraries and tools/Mathematics
Portallike homepages
 Exact Computation: There are functional programming materials too, even with downloadable Haskell source.