scholarly journals Quasi-Rational Analytic Approximation for the Modified Bessel Function I1(x) with High Accuracy

Symmetry ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 741
Author(s):  
Pablo Martin ◽  
Eduardo Rojas ◽  
Jorge Olivares ◽  
Adrián Sotomayor
Keyword(s):  
Asymptotic Expansion ◽  
Bessel Function ◽  
Relative Error ◽  
Asymptotic Series ◽  
Approximation Technique ◽  
Maximum Relative Error ◽  
Analytic Approximation ◽  
Modified Bessel Function ◽  
Elementary Functions ◽  
Order Of Magnitude

A new simple and accurate expression to approximate the modified Bessel function of the first kind I1(x) is presented in this work. This new approximation is obtained as an improvement of the multi-point quasi-rational approximation technique, MPQA. This method uses the power series of the Bessel function, its asymptotic expansion, and a process of optimization to fit the parameters of a fitting function. The fitting expression is formed by elementary functions combined with rational ones. In the present work, a sum of hyperbolic functions was selected as elementary functions to capture the first two terms of the asymptotic expansion of I1(x), which represents an important improvement with respect to previous research, where just the leading term of the asymptotic series was captured. The new approximation function presents a remarkable agreement with the analytical solution I1(x), decreasing the maximum relative error in more than one order of magnitude with respect to previous similar expressions. Concretely, the relative error was reduced from 10−2 to 4×10−4, opening the possibility of applying the new improved method to other Bessel functions. It is also remarkable that the new approximation is valid for all positive and negative values of the argument.

AN ORDERING OF MEASURES OF THE WELFARE COST OF INFLATION IN ECONOMIES WITH INTEREST-BEARING DEPOSITS

2012 ◽  
Vol 16 (5) ◽  
pp. 732-751 ◽  
Author(s):  
Rubens Penha Cysne ◽  
David Turchick
Keyword(s):  
Closed Form ◽  
Relative Error ◽  
Welfare Cost ◽  
Opportunity Costs ◽  
Maximum Relative Error ◽  
Elementary Functions ◽  
Closed Form Solutions ◽  
Welfare Measure ◽  
Welfare Cost Of Inflation ◽  
Alternative Measures

This paper builds on Lucas [Econometrica 68 (2000), 247–274] and on Cysne [Journal of Money, Credit and Banking 35 (2003), 221–238] to derive and order six alternative measures of the welfare costs of inflation (five of them already existing in the literature) for any vector of opportunity costs. We provide examples and closed-form solutions for each welfare measure based both on log–log and on semilog money demands, whenever possible in terms of elementary functions. Estimates of the maximum relative error a researcher can incur when using any of these measures are given. Everything is done for economies with or without interest-bearing deposits.

scholarly journals Exactification of the Poincaré asymptotic expansion of the Hankel integral: spectacularly accurate asymptotic expansions and non-asymptotic scales

2014 ◽  
Vol 470 (2162) ◽  
pp. 20130529 ◽  
Author(s):  
Eric A. Galapon ◽  
Kay Marie L. Martinez
Keyword(s):  
Asymptotic Expansion ◽  
Bessel Function ◽  
Asymptotic Expansions ◽  
Integral Method ◽  
Asymptotic Series ◽  
Poincaré Series ◽  
Poincare Series ◽  
Half Integer ◽  
Distributional Method ◽  
Finite Sum

We obtain an exactification of the Poincaré asymptotic expansion (PAE) of the Hankel integral, as , using the distributional approach of McClure & Wong. We find that, for half-integer orders of the Bessel function, the exactified asymptotic series terminates, so that it gives an exact finite sum representation of the Hankel integral. For other orders, the asymptotic series does not terminate and is generally divergent, but is amenable to superasymptotic summation, i.e. by optimal truncation. For specific examples, we compare the accuracy of the optimally truncated asymptotic series owing to the McClure–Wong distributional method with owing to the Mellin–Barnes integral method. We find that the former is spectacularly more accurate than the latter, by, in some cases, more than 70 orders of magnitude for the same moderate value of b . Moreover, the exactification can lead to a resummation of the PAE when it is exact, with the resummed Poincaré series exhibiting again the same spectacular accuracy. More importantly, the distributional method may yield meaningful resummations that involve scales that are not asymptotic sequences.

scholarly journals The Modified Bessel Function Kn(z)

1919 ◽  
Vol 38 ◽  
pp. 10-19
Author(s):  
T. M. MacRobert
Keyword(s):  
Asymptotic Expansion ◽  
Bessel Function ◽  
Bessel Functions ◽  
Modified Bessel Function ◽  
Definition Of ◽  
Image Position

Gray and Mathews, in their treatise on Bessel Functions, define the function Kn(z) to beWe shall denote this function by Vn(z). This definition only holds when z is real, and R(n)≧0. The asymptotic expansion of the function is also given; but the proof, which is said to be troublesome and not very satisfactory, is omitted. Basset (Proc. Camb. Phil. Soc., Vol. 6) gives a similar definition of the function.

scholarly journals On new approximations for the modified Bessel function of the second kind \(K_0(x)\)

2021 ◽  
Vol 5 (1) ◽  
pp. 11-17
Author(s):  
Francisco Caruso ◽  
◽  
Felipe Silveira ◽  
Keyword(s):  
Bessel Function ◽  
Series Representation ◽  
Modified Bessel Function ◽  
Elementary Functions ◽  
Polynomial Approximations ◽  
Kummer’S Function

A new series representation of the modified Bessel function of the second kind \(K_0(x)\) in terms of simple elementary functions (Kummer's function) is obtained. The accuracy of different orders in this expansion is analysed and has been shown not to be so good as those of different approximations found in the literature. In the sequel, new polynomial approximations for \(K_0(x)\), in the limits \(0< x\leq 2\) and \(2\leq x < \infty\), are obtained. They are shown to be much more accurate than the two best classical approximations given by the Abramowitz and Stegun's Handbook, for those intervals.

Error-aware Design Procedure to Implement Energy-efficient Approximate Squaring Hardware

2020 ◽  
Vol 10 (4) ◽  
pp. 471-477
Author(s):  
Merin Loukrakpam ◽  
Ch. Lison Singh ◽  
Madhuchhanda Choudhury
Keyword(s):  
Energy Saving ◽  
Relative Error ◽  
Energy Efficient ◽  
Piecewise Linear ◽  
Arithmetic Operation ◽  
Design Procedure ◽  
Digital Signal ◽  
Maximum Relative Error ◽  
Square Function ◽  
Efficient Design

Background:: In recent years, there has been a high demand for executing digital signal processing and machine learning applications on energy-constrained devices. Squaring is a vital arithmetic operation used in such applications. Hence, improving the energy efficiency of squaring is crucial. Objective:: In this paper, a novel approximation method based on piecewise linear segmentation of the square function is proposed. Methods: Two-segment, four-segment and eight-segment accurate and energy-efficient 32-bit approximate designs for squaring were implemented using this method. The proposed 2-segment approximate squaring hardware showed 12.5% maximum relative error and delivered up to 55.6% energy saving when compared with state-of-the-art approximate multipliers used for squaring. Results: The proposed 4-segment hardware achieved a maximum relative error of 3.13% with up to 46.5% energy saving. Conclusion:: The proposed 8-segment design emerged as the most accurate squaring hardware with a maximum relative error of 0.78%. The comparison also revealed that the 8-segment design is the most efficient design in terms of error-area-delay-power product.

scholarly journals Eisenstein series and an asymptotic for the K-Bessel function

2021 ◽  
Author(s):  
Jimmy Tseng
Keyword(s):  
Asymptotic Expansion ◽  
Bessel Function ◽  
Eisenstein Series ◽  
Uniform Estimate ◽  
Positive Real ◽  
Dominant Term ◽  
Complex Order ◽  
Fixed Parameter ◽  
Real Argument ◽  
Real Analytic

AbstractWe produce an estimate for the K-Bessel function $$K_{r + i t}(y)$$ K r + i t ( y ) with positive, real argument y and of large complex order $$r+it$$ r + i t where r is bounded and $$t = y \sin \theta $$ t = y sin θ for a fixed parameter $$0\le \theta \le \pi /2$$ 0 ≤ θ ≤ π / 2 or $$t= y \cosh \mu $$ t = y cosh μ for a fixed parameter $$\mu >0$$ μ > 0 . In particular, we compute the dominant term of the asymptotic expansion of $$K_{r + i t}(y)$$ K r + i t ( y ) as $$y \rightarrow \infty $$ y → ∞ . When t and y are close (or equal), we also give a uniform estimate. As an application of these estimates, we give bounds on the weight-zero (real-analytic) Eisenstein series $$E_0^{(j)}(z, r+it)$$ E 0 ( j ) ( z , r + i t ) for each inequivalent cusp $$\kappa _j$$ κ j when $$1/2 \le r \le 3/2$$ 1 / 2 ≤ r ≤ 3 / 2 .

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