How to integrate products of hypergeometric functions and rational functions?

Question

Nicolas Legnazzi 2020-9-13

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/592909-how-to-integrate-products-of-hypergeometric-functions-and-rational-functions

评论： Nicolas Legnazzi 2020-10-2

Hello, I am a physics student and I am new to Matlab. I am trying to solve definite integrals involving the product of confluent first order hypergeometric functions and rational functions as follows:

Where p=0,1,2,3...

When using the Matlab "integral" command the computation of these integrals takes a long time. The question is whether there is any routine in Matlab that does quick calculations of integrals that decay very quickly to zero.

Thank you very much for reading, excuse my English I am using a translator.

2 个评论
显示无隐藏无

David Goodmanson 2020-9-14

Hi Nicolas,

what do you consider to be slow? For p = 0, this takes about 0.1 sec. on my PC. For p > 0, how are you determining the derivative of 1/(q^2+lambda^2) ?

Nicolas Legnazzi 2020-9-15

Hello, thank you very much for your reply. To determine the derivative I apply the command "diff" and iterate it a number p of times. By putting the variables that I quote as m and n in the statement equal to 1 and choosing p = 1 on my PC it takes approximately 10 minutes to calculate that integral.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

David Goodmanson 2020-9-16

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/592909-how-to-integrate-products-of-hypergeometric-functions-and-rational-functions#answer_495274

在 MATLAB Online 中打开

Hello Nicolas,

I don't know how you are implementing the nth derivative of 1/(lambda^2 + q^2) but it is obviously very time consuming. The method below calculates the nth derivative algebraically and takes about as much time as for the zeroth derivative, about 0.1 sec on my PC. That's with moderate values for m, n, alpha, beta, lambda.

lambda = 1.2;
alpha = 2.3;
beta = 3.4;
m = 2;
n = 3;
F = @(q) lorentzdiff(5,q,lambda).*hypergeom(m,3/2,-alpha*q.^2).*hypergeom(n,3/2,-beta*q.^2);
J = integral(F,0,inf)   
% ------------------
function yn = lorentzdiff(n,x,a)
% nth derivative wrt 'a' of the Lorentian 1/(x^2+a^2),
% as a function of x for fixed scalar 'a'
%
% function yn = lorentzdiff(n,x,a)
yn = (-1)^(n)*(factorial(n)./x).*imag((1./(a-i*x)).^(n+1));
ind = abs(x) < 1e-6*a;
yn(ind) = (-1)^n*factorial(n+1)/a^(n+2);
end