Exact real arithmetic

(Difference between revisions)

1 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 numbers-as-programs approaches).

Computable reals can be achieved by many approaches -- it is not one single theory.

1.1 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 Mandelbrot-plotting 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.

1.2 Why are there reals at all which are defined exactly, but are not computable?

See e.g. Chaitin's construction.