What's the formula used for kummerU?
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Hi! Thanks for reading!
I need to write a kummer U function for myself.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1357178/image.png)
But it's only for Re(a)>0 and Re(z)>0, while I want the formula for a<0. So I try to read its source code:
function y = kummerU(a,b,x)
%KUMMERU Kummer's confluent hypergeometric U function.
% U = kummerU(a,b,x) computes the value of Kummer's U function
% U = 1/gamma(a) * int(exp(-x*t)*t^(a-1)*(1+t)^(b-a-1),t,0,inf).
%
% Reference:
% [1] Abramowitz, Milton; Stegun, Irene A., eds., "Chapter 13",
% Handbook of Mathematical Functions with Formulas, Graphs, and
% Mathematical Tables, New York: Dover, pp. 504, 1965.
% Copyright 2014 The MathWorks, Inc.
y = sym.useSymForNumeric(@kummerU, a, b, x);
end
There is nothing for me. So does the function
sym.useSymForNumeric(@kummerU, a, b, x)
There is no str "kummerU" inside it.
So how can I find out how matlab realize kummerU with negative a?
Or it would be better if you know the formula for negative a.
Any suggestion is appreciated!
2 commentaires
Walter Roberson
le 15 Avr 2023
However there are special cases for negative integer a, in which case the formula becomes a polynomial
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Walter Roberson
le 15 Avr 2023
Execute
regexprep(char(evalin(symengine, 'expose(kummerU)')) , '\\n', '\n')
to be shown the formula used.
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