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Two types of tetration : sexp ' > or < 1. - Printable Version +- Tetration Forum (https://tetrationforum.org) +-- Forum: Tetration and Related Topics (https://tetrationforum.org/forumdisplay.php?fid=1) +--- Forum: Mathematical and General Discussion (https://tetrationforum.org/forumdisplay.php?fid=3) +--- Thread: Two types of tetration : sexp ' > or < 1. (/showthread.php?tid=1777) |
Two types of tetration : sexp ' > or < 1. - tommy1729 - 10/11/2023 The chain rule implies for analytic tetration : sexp ' (x) = D exp( sexp(x-1) ) = sexp(x) sexp '(x-1) LET f(0) = 0 , f(x+ 1) = exp(f(x)). then by the above we have f '(0) = f '(1) !! You can check with limits that f ' (0) = f ' (-1) f(0) is consistant AND free to choose. Let f(h) = c h + d h^2 Then f(-1 + h) = ln( c h + d h^2) taking derivatives f ' (-1 + h) = ln© + ln(h) + O(h^2) So f ' (0) = f ' (-1) f(0) is consistant AND free to choose. *** So sexp ' (x) = D exp( sexp(x-1) ) = sexp(x) sexp '(x-1) holds for the full real range as desired. and f '(0) = f '(1) = c where real c is free to choose. You guessed it, I am considering this c as fundamental and cruxial and make a fuss about it. But for some good reasons. I have 2 methods that I feel are important. https://tetrationforum.org/showthread.php?tid=1750 call it the 3/5 method and https://tetrationforum.org/showthread.php?tid=1339 ; the gaussian method. (lemma) As is typical for iterations, for positive integers a : t^[a]( b( t^[-a](x) ) ) somewhat resembles the structure of b(x) (end lemma) Taking that into account it seems that the gaussian method implies 0 < c < 1. If you look at how the gaussian applies to exp^[v](1) it seems to imply lim (exp^[v](1) - 1)/v for small v equals the derivative c. and since erf(x) is such at flat function it seems to imply 0 < c < 1. On the other hand, applying to lemma to the 3/5 method it seems to suggest 1 < c < e - 1 I assume c = 8/5 (or very close) here. ( notice 1 + 3/5 = 8/5 and 8/5 < e-1 ) *** So this seems to prove that the two methods are very different. Notice neither c equals 0. And neither c equals 1 , so a smooth transition from one to the other seems problematic. *** This also seems to implies that the gaussian method does not satisfy the semi-group isomorphism. *** So what property do we prefer ? Well we want that semiexp(semiexp(x)) = exp(x) and we want D_h exp^[h](1) > 1. This seems the case for the 3/5 method. We also want D semiexp(x) > 1 for x > 1. This last inequality leads me to semiexp(x) < (exp(x) + x)/2 for x > 1. Together with the typical semiexp ' (x) > 0 for all real x and semiexp " (x) > 0 for all x > 1 I think this can be achieved by the 3/5 method. *** I start to wonder when variants of the 3/5 method converge to the same solution. Lets say they use the same helper function with also derivative 8/5 at 0. And lets say both of them give a solution semiexp that satisfies the above ( such as sexp ' (x) > 1 for x > 1 ) And lets say such 2 helper functions have a half iterate that both stay close to eachother within ... within what ?? --- To analyse this ... We could consider the third derivative. Or make sharper bounds than (exp(x) + x)/2 I will stop here for now. However I conjecture sexp( slog(x) + w ) = < w exp(x) + (1 - w) x for x > 1 and 1 > w > 0 regards tommy1729 **edited** RE: Two types of tetration : sexp ' > or < 1. - tommy1729 - 10/15/2023 (10/11/2023, 10:58 PM)leon Wrote: The iterates tan(expression + P) and all others that stack variables into functionless categories are a good example that proves both methods are better than the iterates that don't have like umpteen sums in the formulas.Analytic tetration would be missing all of the steps and procedures if more fundamental tetration. And sexp is like Schroeder-Cauchy inversion and inflection more than it operates on P or reconciles the inequality without composite function logic or super function strings. euh what ? regards tommy1729 RE: Two types of tetration : sexp ' > or < 1. - tommy1729 - 10/15/2023 (10/11/2023, 10:25 PM)tommy1729 Wrote: The chain rule implies for analytic tetration : It seems a good idea to consider the slight generalization f(x) = a b^x + c for a > 0 , b > 1 , c >= 0 In particular when f(0) > 1 and/or f ' (0) > 1. Now as you well know exp(x) - 1 is related to tetration base eta ( e^(1/e) ) as a small example. The idea is that the super of f(x) does not have the annoying case above with the repeated derivatives values. So we could demand or investigate bernstein function solutions ( all derivatives > 0 ) for the superfunctions at a larger domain/range. For instance f(x) = 2 exp(x) F(0) = 0 F(x+1) = 2 exp(F(x)) and then D^n F(x) >= 1 for x > 0 I need to think more about it, but I wanted to share this. Notice 2 exp(x) - 2 exp(- 3/5 x) can be used as replacement for the 3/5 method. and the same idea for the gaussian method. regards tommy1729 RE: Two types of tetration : sexp ' > or < 1. - tommy1729 - 10/17/2023 Ok here is an idea for uniqueness or at least putting solutions in category. f(x) is an analytic function on [0,oo] such as analytic semiexp(x) or tet(x), so the idea is general. More specific Let f^{n} mean n th derivative of f. say f(z) satisfies f(0) = 0 f(1) = 1 f(x+1) = exp(f(x)) f ' (0) = f '(1) = c ( a given c ) then TR( f(x) ) = integral from 1 to infinity sum_(n>=0) (f^{n}(x))^(-2) dx LET Min TR( f(x) , c ) = G© where the minimum is for a fixed c , and f(x) is picked to get a minimum value. Then we wonder what G© is as a function of c. And how many analytic solutions f(x) exist with the same G© value. We can further wonder what value of c makes G© at minimum. Notice that TR can diverge for non tetration like functions. Adding a weight might help there. the details for systematic adding weights needs to be investigated. regards tommy1729 |