On 16/07/2015 17:17, Ian Kelly wrote:
On Thu, Jul 16, 2015 at 3:28 AM, Robin Becker <ro...@reportlab.com> wrote:
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I believe the classic answer is Ackermann's function
http://demonstrations.wolfram.com/RecursionInTheAckermannFunction/
which is said to be not "primitive recursive" ie cannot be unwound into
loops; not sure whether that implies it has to be recursively defined or can
perhaps be broken down some other way.
that should have said "simple loops"
My recollection -- and it's been awhile since I've studied
computability theory so I may be distorting things here -- is that
primitive recursive functions can be computed using for loops, i.e.
loops where the number of iterations is bounded in advance, whereas
non-primitive recursive functions require while loops.
I'm guessing, but is the implication that for loops can be specified finitely in
advance, but while loops need some processing in the calculation to determine
termination? I'm an engineer :(
--
Robin Becker
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