4 ms·
This might not be the best written or best sourced article, but I would start here: https://en.wikipedia.org/wiki/Computable_analysis https://en.wikipedia.org/w
by ogogmad 4y ago
This might not be the best written or best sourced article, but I would start here: https://en.wikipedia.org/wiki/Computable_analysis https://en.wikipedia.org/wiki/Computable_analysis
Most operations for defining real numbers are computable. The reason for this is that, in practice, continuous functions and functionals are the same thing as computable functions and functionals. Continuous functions which aren't computable are generally pathological curiosities. One consequence of this heuristic is that since the Riemann integral is a continuous functional, one might guess that it is also computable. Indeed it is (but the proof isn't obvious). This then implies the computability of the constant pi because pi is equal to the integral
1
⌠
⎮ ________
⎮ ╱ 2
⎮ 2⋅╲╱ 1 - x dx
⌡
-1
The computability of integration implies the computability of root-finding because one can use the argument principle to do it.
- Someone 4y ago> Most operations for defining real numbers are computable. Isn’t that a tautology or at least selection bias? “Operation” seems to imply we can carry it out, which means the number can be computed. Even if we give “operation” a wider meaning to include those that can’t be carried out, are we deceiving ourselves that most of them are computable because most of those we have thought of in the history of mathematics are? Or do we really know something about the cardinalities of those sets?
- pfdietz 4y agoAnd the total number of such definitions is countable (since each definition is a finite sequence of symbols from a finite alphabet). Therefore, the number of such definable real numbers is countable. Any real number will be arbitrarily close to a definable number (all rational numbers are definable in this sense) though.