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 Newtonian Tetration fivexthethird Junior Fellow Posts: 9 Threads: 3 Joined: Nov 2013 01/14/2014, 11:03 AM I'm not too sure what the exact term for this type of tetration is, but you'll probably recognize it as the newton series ${\ ^x} b = \sum^\infty _{k=0} {x\choose{k}}\Delta^k \text{sexp}_b(0)$ Where $\Delta f(x)$ is the difference operator $f(x+1) - f(x)$. The above series has two main problems: 1. It has horrifyingly bad convergence 2. It only converges for bases $1 The first has two solutions: 1.Expanding around -1 instead of 0 actually seems to help convergence. Not a lot, but it does help. 2.The series seems to converge faster at larger arguments. This can be exploited by taking the logarithm of the series and increasing the argument appropriately. This helps tremendously, with 40 logs and 190 terms, $\ ^{\frac{1}{2}}\sqrt{2}$ has 40 correct digits. Without the logs, it only has 4. This ends up allowing this tetration be be calculated fast and accurately enough that we can help solve the second problem by taylor expanding the in the base. Thus, here are the first 20 coefficients of $\ ^{\frac{1}{2}}x$ around 1.3: Code:1.18938676815057446038958978533952183643013189670322056055481057298164131225527684427735915948183638577039636148478045857061959630059209396667384426975, 0.502010375341689917463980699942849515217180567032456403096253323808817519839299401993748785203409898436669803385695469896066815361054606935920440249897, -0.262759788721756864581601122842893801277751036360441951655201206112118171206055203331662497461495616704883313354811962146537537522652596017799716984049, 0.252541433354585431957607810065749107577232333317254003936920345075890384451085222527914626348907743064183299869580062147394545557290468315440354334807, -0.352612282449298556037058962871272764222633755255262271381414574681831425906537015507092391324710037580722776608642134517129513748910717693940021788039, 0.621677298164652736531936223803703122798845331895259122967269609718567408818646902493674955196358849620675027493712391738200958924868991814377511409157, -1.26050780940949293309473496751457508803155869212975193602873050623150572857720148361865858042292939837099015175537045195113300841486392202214221157598, 2.78946894926307250419609012944237141327971047365764644180937634359092733505462942006856627879977802915804677312596759441403910348973540678219087075504, -6.55130450767494919665255117058858039633497329452433984571224787280239805541843479702057849808492419468918495110076687736921823268369546258458551623048, 16.0710090228845933132534615450640023013886687687167747617039630933751129706165865500814356888785226546490852687225827248617581496737696817168093153429, -40.7704259182153375530604086443593919521475614769493253756483954258517708616052988082048357384027386210545375335546113749939214696714432741264720158991, 106.244321126292059196752083390024857789027574924140570504522491688951114502955395593102728514269806301547513915489115405515891366398589937001672403523, -283.023065848868812346563707317507012808599394093222261325251615876830618173347110349520513434919295375400097755630023208473741240599411576425055827909, 767.933763786027965831407740576122497561217686342251260748284176663708140871513390685625726433475251079261484458238695383917961576775641177247147520503, -2116.44561270241051080236792320537583316910647423316698320246454576890631421345287600136864420938113116159861645314023708929380344723655318159752190274, 5911.8594138127759329749422943752047603337761813433546786311935528993537980987722892605576055010848848272468910526372583051327151512324971334609620443, -16707.3334717021267293040481463596170312951888040432337228406433675057696360597132222789111854366949803489111005938596369105185867941219689060361131505, 47700.5349235131417564363370889439820833084022424615928142803634329053272283017103738924412877180486952747228851252753475003864826221543486125144067987, -137421.741181992684270720845646461088437555676807641552339277946116606194777054566765162517003931685067266949282565592941858857284964758394951437621541, 399099.764178539676938227138702779209771226135938677676356183560670501048089604499650618860208276875975877505538229622254784064064072823768230700329241, -1167441.59720175702159986672888446578396885416629335195276020166949794005477053704724756023751465315420620439408155825183831357730080864875865877178256I estimate that those are accurate to around 30 coefficients The series seems to have a radius of convergence of around .4 Gottfried Ultimate Fellow Posts: 776 Threads: 121 Joined: Aug 2007 01/24/2014, 10:04 PM (This post was last modified: 01/24/2014, 10:05 PM by Gottfried.) Hi Fivexthethird - perhaps this might be interesting for you: I've made a discussion of the Newtonian method in comparision with the diagonalization-approach in 2008; perhaps today I could write this better (but unfortunately usually don't have time for this); see here: http://go.helms-net.de/math/tetdocs/Bino...zation.htm I came to tetration via consideration of infinite matrices and powers of them, so possibly the whole article looks strange to you but I hope it is self-expalining enough. Don't hesitate to ask if something might look explainable by not too much effort... Gottfried Gottfried Helms, Kassel « Next Oldest | Next Newest »

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