How do I cite this document and does it say what I think it says? - Printable Version +- Tetration Forum ( https://math.eretrandre.org/tetrationforum)+-- Forum: Tetration and Related Topics ( https://math.eretrandre.org/tetrationforum/forumdisplay.php?fid=1)+--- Forum: Mathematical and General Discussion ( https://math.eretrandre.org/tetrationforum/forumdisplay.php?fid=3)+--- Thread: How do I cite this document and does it say what I think it says? ( /showthread.php?tid=1199) |

RE: How do I cite this document and does it say what I think it says? - Chenjesu - 09/10/2018
(09/10/2018, 03:00 PM)sheldonison Wrote:So I don't understand exactly what this wseries and xpoint is supposed to mean, I've never seen anyone use that notation. If it exists then what is relevant is a typical Taylor series (or some kind of functional series) just with a standard sum from n_0 to infinity for the -1 branch and that's it, nothing fancy, no fixed points or computational approximations.(09/10/2018, 12:27 PM)Chenjesu Wrote: I appreciate the work but the question was not limited to fixed points since the W function has a more general relationship to tetration. I looked on wikipedia and noticed that for some reason the Taylor series for the -1 branch is drastically more complicated, and so I was wondering if it has a simpler series representation. RE: How do I cite this document and does it say what I think it says? - sheldonison - 09/10/2018
(09/10/2018, 06:50 PM)Chenjesu Wrote: So I don't understand exactly what this wseries and xpoint is supposed to mean, I've never seen anyone use that notation. If it exists then what is relevant is a typical Taylor series (or some kind of functional series) just with a standard sum from n_0 to infinity for the -1 branch and that's it, nothing fancy, no fixed points or computational approximations. wseries is just the Taylor series from this paper[45] ; we can express LambertW as follows where for negative z the +sqrt is the (-1) branch the Op asked about. I'm not sure what non-standard notation I'm using; this is just function composition ... Post#28 has the first 16 terms of the wseries Taylor series. The recursive formula for the coefficients was provided in post#30. wseries has the same a_3 to a_oo Taylor series coefficients as my xfixed series from post#27 which is before I discovered Corless's paper. My best guesss is that perhaps Chenjesu just views this as too complicated a solution, and he is looking for a simpler series. The simpler LambertW Taylor series for the main branch at z=0 only has a radius of convergence of 1/e, and won't work for the fixed points of any base>exp(1/e). So if that is Chenjesu's complaint, then yes, this is a more complicated series, but it is much more powerful since it gives the both the main branch and the (-1) branch, and since it converges for a fairly large subset of the complex plane. Since the (-1) branch is only real valued at the real axis from -1/e to 0, and it has a really complicated singularity at 0, so there is no hope of getting any series in x centered at x=0. Since the (-1) branch also has a square root branch at -1/e, that requires a square root term in the composition, so that can't be a simple series either. There probably aren't any other rational x,W(x) pairings besides at -1/e. The approach from Corless's paper has rational coefficients, and a square root in the substitution and is re-centered so that z=-1/e is mapped to zero; that might be the best that we can do for the (-1) branch. |