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 Crazy power series in terms of base e andydude Long Time Fellow Posts: 509 Threads: 44 Joined: Aug 2007 04/23/2009, 06:12 AM The power series expansions of tetration ${}^{z}a$ about the base are commonly discussed about (a=1), which produce very nice coefficients. However, I remembered that the same power series about other points made each coefficient depend on tetration, which isn't so bad if we already know one base. I'm not sure if this is useful for noninteger heights, because there are z's in the bounds for summation. $ \begin{tabular}{rl} {}^{z}a & = {}^{z}e \\ & + \left[ \frac{1}{e} \sum_{k=1}^{z} \prod_{j=0}^{k} {}^{(z-j)}e \right] (a - e) \\ & + \left[ \frac{1}{e^2}\sum_{k=1}^{z} \left( e(k-1) - 1 + \sum_{j=0}^{k} \frac{1}{{}^{z-j}e} \sum_{i=1}^{z-j} \prod_{l=0}^{i} {}^{z-j-l}e \right) \prod_{j=0}^{k} {}^{z-j}e \right] (a - e)^2 \\ & + \cdots \end{tabular}$ Pretty crazy... Andrew Robbins Gottfried Ultimate Fellow Posts: 789 Threads: 121 Joined: Aug 2007 06/13/2009, 05:46 AM (This post was last modified: 06/13/2009, 05:51 AM by Gottfried.) (04/23/2009, 06:12 AM)andydude Wrote: if we already know one base. I'm not sure if this is useful for noninteger heights, because there are z's in the bounds for summation.Hi Andrew - besides the rest of the formula (): there is an article of Markus Müller, Berlin, about sums with fractional bounds. Perhaps there is something interesting for you... Gottfried seeindex) : http://www.math.tu-berlin.de/~mueller/research.html M. Müller, D. Schleicher, "Fractional Sums and Euler-like Identities", http://www.arxiv.org/abs/math/0502109 M. Müller, D. Schleicher, "How to add a non-integer number of terms, and how to produce unusual infinite summations", Journal of Computational and Applied Mathematics, Vol 178/1-2 pp 347-360 (2005), HowToAdd.pdf Gottfried Helms, Kassel bo198214 Administrator Posts: 1,395 Threads: 91 Joined: Aug 2007 06/14/2009, 04:49 PM (06/13/2009, 05:46 AM)Gottfried Wrote: M. Müller, D. Schleicher, "Fractional Sums and Euler-like Identities", http://www.arxiv.org/abs/math/0502109 M. Müller, D. Schleicher, "How to add a non-integer number of terms, and how to produce unusual infinite summations", Journal of Computational and Applied Mathematics, Vol 178/1-2 pp 347-360 (2005), HowToAdd.pdf Thank you Gottfried for the references. The base idea was independently mentioned by Ansus on the forum: http://math.eretrandre.org/tetrationforu...31#pid3131 For monomials we have a closed form for the (indefinite) sum. Also we know that the sum is linear. So we can compute the sum of polynomials and even powerseries. tommy1729 Ultimate Fellow Posts: 1,493 Threads: 356 Joined: Feb 2009 06/14/2009, 11:40 PM (06/14/2009, 04:49 PM)bo198214 Wrote: (06/13/2009, 05:46 AM)Gottfried Wrote: M. Müller, D. Schleicher, "Fractional Sums and Euler-like Identities", http://www.arxiv.org/abs/math/0502109 M. Müller, D. Schleicher, "How to add a non-integer number of terms, and how to produce unusual infinite summations", Journal of Computational and Applied Mathematics, Vol 178/1-2 pp 347-360 (2005), HowToAdd.pdf Thank you Gottfried for the references. The base idea was independently mentioned by Ansus on the forum: http://math.eretrandre.org/tetrationforu...31#pid3131 For monomials we have a closed form for the (indefinite) sum. Also we know that the sum is linear. So we can compute the sum of polynomials and even powerseries. however , the non-integer number of additions in the pdf is just a possible generalisation. so it might not be tetration afterall , or beter said , not neccessarily your " favorite " tetration. regards tommy1729 « Next Oldest | Next Newest »

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