How to Extend the Sum of Any* Function

Video Description

In this video, we define a general way to sum a fractional, irrational, or even complex number of terms. Along the way we discover some key concepts from discrete calculus. This is an extension of the method of my first two videos: Extending the Harmonic Numbers to the Reals: https://www.youtube.com/watch?v=9p_U_o1pMKo How to Take the Factorial of Any Number: https://www.youtube.com/watch?v=v_HeaeUUOnc After uploading this video, I learned that this method has been independently discovered by Jean-Luc Marichal and Naïm Zenaïdi. They explore it thoroughly in their open-access book, "A Generalization of Bohr-Mollerup's Theorem for Higher Order Convex Functions": https://link.springer.com/book/10.1007/978-3-030-95088-0 Articles referenced in this video: Müller, M., & Schleicher, D. (2011). How to Add a Noninteger Number of Terms: From Axioms to New Identities. The American Mathematical Monthly, 118(2), 136–152. https://doi.org/10.4169/amer.math.monthly.118.02.136 https://www.tandfonline.com/doi/abs/10.4169/amer.math.monthly.118.02.136 arXiv: https://arxiv.org/abs/1001.4695 Müller, M., & Schleicher, D. (2005). How to add a non-integer number of terms, and how to produce unusual infinite summations. Journal of Computational and Applied Mathematics, 178(1–2), 347–360. https://doi.org/10.1016/j.cam.2004.08.009 https://www.sciencedirect.com/science/article/pii/S0377042704003851 Müller, M., Schleicher, D. Fractional sums and Euler-like identities. Ramanujan J 21, 123–143 (2010). https://doi.org/10.1007/s11139-009-9214-9 https://link.springer.com/article/10.1007/s11139-009-9214-9 arXiv: https://arxiv.org/abs/math/0502109 The identities at 37:57 can be found on Markus Müller's website: https://mpmueller.net/fractional-sums/ This video was created with Manim: Community edition: https://www.manim.community/ All the code for this video is available on GitHub: https://github.com/LinesThatConnect/How-to-Extend-the-Sum-of-Any-Function Music credits: - Night Music by Kevin Macleod - river - Calm and Relaxing Piano Music by HarumachiMusic - akebono by Sayuri Hayashi Egnell - Between Moments by Amber Glow - Clockmaker's Daydream by 369 - Observations by From Now On - Particle Emission by Silver Maple - Pyrite by Harbours Oceans - The Farmhouse by Silver Maple - Threads by Ever So Blue - The Fog by Lines That Connect - Heavy Head, Light Rain by Lines That Connect - Thanks for Watching by Lines That Connect The three songs by me can be found on Soundcloud: https://soundcloud.com/lines-that-connect Chapters: 00:00 Intro 1:31 Notes About This Video 2:53 Stating the Problem 4:09 The Recursive Formula 5:52 Going to the Right 7:23 Deriving the Main Formula 10:55 The First Solution 12:57 Flattening Out 14:56 The Forward Difference 16:11 Deriving the Iterated Forward Difference Formula 17:30 The Second Solution 20:18 High Order Forward Differences 23:07 The General Solution 27:01 Nasty Nested Sums 34:04 The General Solution, For Real 36:39 What You Came Here For 37:26 The Published Solution 42:59 Comparing the Solutions 44:58 The Gregory-Newton Formula 45:43 Thanks for Watching!