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å ã 㯠Ramanujan ã Ramanujan ã®å ¬å¼ ãçºè¡¨ãã¦ããç 究ããå§ããå ¬å¼ã§ããã Borwein[FB05] ã®ç 究ãã AGM ç³»ã¨åæ§ã® æ¥åç©åã«å ããä¿åå½¢å¼ã¨é¢é£ããã¦çµã¿ç«ã¦ãããã[FT01] ããç§ã¯ãã®åéã«æãããªãã®ã§è©³ç´°ãªè¨åã¯æ¢ãã¦ããã
Ramanujan ã®å ¬å¼ãåºãããå½æã¯é çªã«è¨ç®ãã¦ãã $O(n^2)$ ã®æ¹æ³ããç¥ããã¦ããªãã£ããã Binary Splitting æ³ ã DRM æ³ã使ãããããã«ãªã£ã¦ãã㯠$O(n(\log n)^3)$ ç¨åº¦ã®è¨ç®éã«ãªããã¨ã ä¿æ°ãå«ããå®è¨ç®ã³ã¹ããå°ãªããªããã¨ãç¥ããã ç¾å¨ç¥ããã¦ããä¸ã§æéã®è¨ç®æ¹æ³ã¨ãªã£ã¦ããã [JT01][JT03][JM01]
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Ramanujan ã®å ¬å¼
\[ \frac{1}{\pi} = \frac{\sqrt{8}}{9801}\sum_{n=0}^{\infty} \frac{(4n)!(1103+26390n)}{(n!)^4 \cdot 396^{4n}} \]å®æ°ã®ç´ å æ°å解㯠$9801=3^4\cdot11^2$ã$396=2^2\cdot3^2\cdot11$ã$26390=2\cdot5\cdot7\cdot13\cdot29$ ã¨ãªã£ã¦ããã$\sum$ ã® 1 é ãããç´ 8 æ¡ç²¾åº¦ãä¸ããã
Ramanujan ã®å ¬å¼ (2)
\[ \frac{1}{\pi} = \frac{1}{3528}\sum_{n=0}^{\infty} \frac{(-1)^n(4n)!(1123+21460n)}{(n!)^4 \cdot 14112^{2n}} \]ãã¡ãã¯å¹³æ¹æ ¹ã使ããªãå½¢ã®å ¬å¼ã§ããã å®æ°ã®ç´ å æ°å解㯠$3528=2^3\cdot3^2\cdot7^2$ï¼$14112=2^5\cdot3^2\cdot7^2$ï¼ $21460=2^2\cdot5\cdot29\cdot37$
Chudnovsky ã®å ¬å¼
\[ \frac{1}{\pi} = \frac{12}{\sqrt{C^3}}\sum_{n=0}^{\infty} \frac{(-1)^n(6n)!(A+Bn)}{(3n)!(n!)^3C^{3n}} \] \[ \begin{eqnarray} A &=& 13591409 &=& 13\cdot1045493\\ B &=& 545140134 &=& 2\cdot3^2\cdot7\cdot11\cdot19\cdot127\cdot163\\ C &=& 640320 &=& 2^6\cdot3\cdot5\cdot23\cdot29 \end{eqnarray} \]ç¾å¨ç¥ããã¦ããæéã®è¨ç®æ段ã¯ãã®å ¬å¼ã« Binary Splitting æ³ ã DRM æ³ãé©ç¨ããæ段ã§ããã $\sum$ ã® 1 é ãããç´ 14 æ¡ç²¾åº¦ãä¸ããã
Borwein ã®å ¬å¼
\[ \frac{1}{\pi} = \frac{12}{\sqrt{C^3}}\sum_{n=0}^{\infty} \frac{(-1)^n(6n)!(A+Bn)}{(3n)!(n!)^3C^{3n}} \] \[ \begin{eqnarray} A &=& 1657145277365+212175710912\sqrt{61}\\ &=& 5\cdot149\cdot2224356077 + 2^6\cdot11^3\cdot293\cdot8501\sqrt{61}\\ B &=& 107578229802750+13773980892672\sqrt{61}\\ &=& 2\cdot3^2\cdot5^3\cdot7\cdot23\cdot61\cdot71\cdot191\cdot359 + 2^9\cdot3^2\cdot7\cdot11^3\cdot13\cdot23\cdot29\cdot37 \sqrt{61}\\ C &=& 5280(236674+30303\sqrt{61})\\ &=& 2^5\cdot3\cdot5\cdot11( 2\cdot17\cdot6961 + 3^2\cdot7\cdot13\cdot37\sqrt{61}) \end{eqnarray} \]$A$ã$B$ã$C$ ã®å¤ã¯éãããåºæ¬çã«ã¯ Chudnovsky ã®å ¬å¼ã¨åãå½¢ããã¦ããã
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ä¸è¨ã®éããç¾å¨æéã®å ¬å¼ã¨ãã¦ç¥ããã Chudnovsky ã®å ¬å¼ã¯ åºå ¸ã«ãã£ã¦æ¸ãæ¹ã«å°ãããªã¨ã¼ã·ã§ã³ãåå¨ããã ããããªãããå ¨ã¦ã®å ¬å¼ã¯çµå±ã®ã¨ããè¦ãããéãã ãã§æ°å¼èªä½ã¯åãã§ããã
\[ \frac{1}{\pi} = \frac{12}{\sqrt{C^3}}\sum_{n=0}^{\infty} \frac{(-1)^n(6n)!(A+Bn)}{(3n)!(n!)^3C^{3n}} = \frac{12}{\sqrt{C^3}}\sum_{n=0}^{\infty} K_n(A+Bn) \] \[ K_n = \frac{(-1)^n(6n)!}{(3n)!(n!)^3C^{3n}} \]ã¨ããã¨ã
\[ \begin{eqnarray} \frac{K_{n+1}}{K_n} &=& \frac{-1\cdot(6n+6)(6n+5)(6n+4)(6n+3)(6n+2)(6n+1)} {(3n+3)(3n+2)(3n+1)(n+1)^3C^3}\\ &=&\frac{-24(6n+5)(2n+1)(6n+1)}{C^3(n+1)^3} \end{eqnarray} \]ã¨ãªãã®ã§ã
\[ \begin{eqnarray} \frac{1}{\pi} &=& \frac{12}{\sqrt{C^3}} \sum_{n=0}^{\infty}(A+Bn) \prod_{k=0}^{n-1} \frac{K_{k+1}}{K_k}\\ &=& \frac{12}{\sqrt{C^3}} \sum_{n=0}^{\infty}(A+Bn) \prod_{k=0}^{n-1} \frac{-24(6k+5)(2k+1)(6k+1)}{C^3(k+1)^3}\\ &=& \frac{12}{\sqrt{C^3}} \left(A+\frac{K_1}{K_0} \left(A+B+\frac{K_2}{K_1} \left( \cdots \left(A+nB + \frac{K_{n+1}}{K_n} \left( \cdots \right) \cdots \right. \right. \right. \right) \end{eqnarray} \]ãªã©ã®å½¢ãå°ãããã