|
16 | 16 | For example, |
17 | 17 | \input{sections/figures/05_fig_coefficients_a} |
18 | 18 |
|
19 | | -Essentially, the polynomial $P(m, X, N)$ is a result of rearrangement inside Faulhaber's formula. |
| 19 | +Essentially, the polynomial $P(m, X, N)$ is derived from a rearrangement of Faulhaber's formula. |
20 | 20 | It was inspired by Knuth's \textit{Johann Faulhaber and sums of powers}, see~\cite{knuth1993johann}. |
21 | 21 | In particular, the polynomial $P(m, X, N)$ yields an identity for odd powers |
22 | 22 | \begin{align*} |
23 | 23 | P(m, X, X) = X^{2m+1} |
24 | 24 | \end{align*} |
25 | | -In extended form |
| 25 | +In its extended form |
26 | 26 | \begin{align*} |
27 | 27 | X^{2m+1} = \sum_{r=0}^{m} \sum_{k=1}^{X} \coeffA{m}{r} k^r (X-k)^r |
28 | 28 | \end{align*} |
29 | | -Precisely, the relation between Faulhaber's formula and $P(m,X,N)$ is shown by~\cite{kolosov2025unexpected}. |
| 29 | +The exact relation between Faulhaber's formula and $P(m,X,N)$ is shown by~\cite{kolosov2025unexpected}. |
30 | 30 |
|
31 | | -However, apart polynomial identity for odd powers, I've spotted several approximation properties of $P(m,X,N)$. |
32 | | -Therefore, in this manuscript we discuss approximation properties of polynomial $P(m,X,N)$. |
| 31 | +However, apart from the polynomial identity for odd powers, I've discovered several approximation properties of $P(m,X,N)$. |
| 32 | +Therefore, in this manuscript we explore the approximation properties of the polynomial $P(m,X,N)$. |
33 | 33 | I use a few well-known criteria to measure and estimate error of approximation: Absolute error, Relative error and |
34 | 34 | Percentage error. |
35 | | -Assume that function $f_2(x)$ approximates the function $f_1 (x)$ then the errors are |
36 | | - |
| 35 | +Assume that the function $f_2(x)$ approximates the function $f_1 (x)$, then errors are given by |
37 | 36 | \begin{align*} |
38 | 37 | \mathrm{Absolute \; Error} &= \lvert f_1(x) - f_2(x) \rvert \\ |
39 | 38 | \mathrm{Relative \; Error} &= \frac{\lvert f_1(x) - f_2(x) \rvert}{\lvert f_1(x) \rvert} \\ |
40 | 39 | \mathrm{Percentage \; Error} &= \frac{\lvert f_1(x) - f_2(x) \rvert}{\lvert f_1(x) \rvert} \times 100\% |
41 | 40 | \end{align*} |
42 | 41 |
|
43 | | -Diving straight to the point, we switch our focus to already mentioned polynomial $P(2,X,4) = 900X^2 - 6000X + 10624$ |
| 42 | +Diving straight into the point, we switch our focus to the previously mentioned polynomial |
| 43 | +$P(2,X,4) = 900X^2 - 6000X + 10624$ |
44 | 44 | to show the first example of how it approximates the odd power function $X^5$. |
45 | | -In fact, we approximate the polynomial $X^{2m+1}$ by lower degree polynomial $X^m$ as the following image presents |
| 45 | +In fact, we approximate the polynomial $X^{2m+1}$ using a lower-degree polynomial of degree $m$, |
| 46 | +as shown in the following image |
46 | 47 | \begin{figure}[H] |
47 | 48 | \centering |
48 | 49 | \includegraphics[width=1\textwidth]{sections/images/03_plots_polynomial_p2_n4_with_fifth} |
49 | | - ~\caption{Polynomial plot $P(2, X, 4)$ with fifth power $X^5$. |
| 50 | + ~\caption{Approximation of fifth power $X^5$ by $P(2, X, 4)$. |
50 | 51 | Points of intersection $X=4$, $X=4.42472$, $X=4.99181$. |
51 | | - Convergence interval: $4.0 \leq X \leq 5.1$ with percentage error $E < 1\%$. |
| 52 | + Convergence interval is $4.0 \leq X \leq 5.1$ with percentage error $E < 1\%$. |
52 | 53 | }\label{fig:03_plots_polynomial_p2_n4_with_fifth} |
53 | 54 | \end{figure} |
54 | | -As we see, polynomial $P(2, X, 4)$ approximates $X^5$ in a neighborhood of $N=4$ with |
55 | | -the convergence interval $4.0 \leq X \leq 5.1$ that has percentage error lesser than $1\%$ which is quite impressive. |
56 | | -%Therefore, having fixed $N=4$ the polynomial $P(2, X, 4)$ approximates odd power in neighborhood of $N=4$ |
57 | | -%which is $3.9 \leq X \leq 5.3$. |
58 | | -Consider the table below to showcase the concrete values of absolute, relative and percentage errors of this approximation |
| 55 | +As observed, the polynomial $P(2, X, 4)$ approximates $X^5$ in the neighborhood of $N=4$ with |
| 56 | +the convergence interval $4.0 \leq X \leq 5.1$ where the percentage error is less than $1\%$ which is quite remarkable. |
| 57 | +The following table presents specific values of absolute, relative, and percentage errors for this approximation |
59 | 58 | \input{sections/figures/032_polynomials_p2_table_n4} |
60 | 59 |
|
61 | | -One more interesting observation can be done by increasing the value of $N$ in $P(m, X, N)$ having fixed $m$, it |
62 | | -follows that by increasing $N$ the length of convergence interval with odd-power $X^{2m+1}$ increasing as well. |
| 60 | +One more interesting observation arises by increasing the value of $N$ in $P(m, X, N)$ while keeping $m$ fixed. |
| 61 | +As $N$ increases, the length of the convergence interval with the odd-power $X^{2m+1}$ also increases. |
63 | 62 | For instance, |
64 | 63 | \begin{itemize} |
65 | | - \item Having $P(2, X, 4)$ and $X^5$ the convergence interval with percentage error lesser than $1\%$ is $4.0 \leq X \leq 5.1$ with lenght of interval $L=1.1$ |
66 | | - \item Having $P(2, X, 20)$ and $X^5$ the convergence interval with percentage error lesser than $1\%$ is $18.7 \leq X \leq 22.9$ with lenght of interval $L=4.2$ |
67 | | - \item Having $P(2, X, 120)$ and $X^5$ the convergence interval with percentage error lesser than $1\%$ is $110.0 \leq X \leq 134.7$ with lenght of interval $L=24.7$ |
| 64 | + \item For $P(2, X, 4)$ and $X^5$, the convergence interval with a percentage error less than $1\%$ is $4.0 \leq X \leq 5.1$, with a length $L=1.1$ |
| 65 | + \item For $P(2, X, 20)$ and $X^5$, the convergence interval with a percentage error less than $1\%$ is $18.7 \leq X \leq 22.9$, with a length $L=4.2$ |
| 66 | + \item For $P(2, X, 120)$ and $X^5$, the convergence interval with a percentage error less than $1\%$ is $110.0 \leq X \leq 134.7$, with a length $L=24.7$ |
68 | 67 | \end{itemize} |
69 | | -The reason why the lenght of convergence interval rises as $N$ rise lays beneath the implicit form of polynomial $P(m,X,N)$ |
| 68 | + |
| 69 | +The reason behind this behavior lies in the implicit form of the polynomial $P(m,X,N)$, |
70 | 70 | meaning that |
71 | 71 | \begin{align*} |
72 | 72 | P(m,X,N) = \sum_{r=0}^{m} (-1)^{m-r} U(m, N, r) \cdot X^{r} |
|
75 | 75 | \begin{align*} |
76 | 76 | U(m, N, r) = (-1)^m \sum_{k=1}^{N} \sum_{j=r}^{m} \binom{j}{r} \coeffA{m}{j} k^{2j-r} (-1)^j |
77 | 77 | \end{align*} |
78 | | -which rises as $N$ rise. |
| 78 | +which grows as $N$ increases. |
| 79 | +Few cases of coefficients $U(m, N, r)$ are registered as OEIS sequences~\cite{ |
| 80 | + oeis_coefficients_u_m_l_k_defined_by_polynomial_identity_1, |
| 81 | + oeis_coefficients_u_m_l_k_defined_by_polynomial_identity_2, |
| 82 | + oeis_coefficients_u_m_l_k_defined_by_polynomial_identity_3}. |
79 | 83 |
|
80 | | -To wrap up the current state of the manuscript, refresh the key facts and finding we got so far. |
81 | | -Therefore, the polynomial $P(m,X,N)$ is an $m$-degree polynomial in $X \in \mathbb{R}$, having fixed non-negative |
82 | | -integers $m$ and $N$. |
83 | | -It approximates odd power function $X^{2m+1}$ in some neighborhood of fixed $N$. |
84 | | -The length $L$ of convergence interval between $X^{2m+1}$ and $P(m,X,N)$ rises as $N$ rise. |
| 84 | +To summarize, let us recap the key findings so far. |
| 85 | +The polynomial $P(m,X,N)$ is an $m$-degree polynomial in $X \in \mathbb{R}$ with fixed non-negative integers $m$ and $N$. |
| 86 | +It approximates the odd power function $X^{2m+1}$ within a specific neighborhood of $N$. |
| 87 | +The length $L$ of the convergence interval between $X^{2m+1}$ and $P(m,X,N)$ increases as $N$ grows. |
85 | 88 |
|
86 | 89 | For the sake of clear and precise verification of results, I attach mathematica programs to generate |
87 | 90 | plots and data tables, so that reader is able to verify the main results of current part of manuscript, |
|
94 | 97 | \begin{figure}[H] |
95 | 98 | \centering |
96 | 99 | \includegraphics[width=1\textwidth]{sections/images/07_plot_of_6th_power_with_p_2_4_times_x} |
97 | | - ~\caption{Polynomial plot $P(2, X, 4)\cdot X$ with sixth power $X^6$. |
98 | | - Convergence interval: $3.9 \leq X \leq 5.1$ with percentage error $E < 3\%$. |
| 100 | + ~\caption{Approximation of sixth power $X^6$ by $P(2, X, 4) \cdot X$. |
| 101 | + Convergence interval is $3.9 \leq X \leq 5.1$ with percentage error $E < 3\%$. |
99 | 102 | }\label{fig:07_plot_of_6th_power_with_p_2_4_times_x} |
100 | 103 | \end{figure} |
101 | 104 | Therefore, we have reached the statement that |
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