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I'd like to convert

MeijerG[{{}, {1., 1.}}, {{0., 0., 4.}, {}}, -1. T λ]

to its Standard Functions (For example Bessel function or ...). Any suggestion?

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1 Answer 1

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From the documentation on MeijerG,

Use FunctionExpand to expand MeijerG into simpler functions:

FunctionExpand@
 MeijerG[{{}, {1, 1}}, {{0, 0, 4}, {}}, -T λ]

(* -11 + 11 E^(T λ) + 6 EulerGamma - 
 5 E^(T λ) T λ + E^(T λ) T^2 λ^2 + 
 6 (11/6 - EulerGamma - Log[-T λ]) + 6 Log[-T λ] + 
 6 (-ExpIntegralEi[T λ] - Log[-T λ] + 
    1/2 (-Log[1/(T λ)] + Log[T λ])) *)

Note this doesn't work if you use floats instead of integers,

FunctionExpand@
 MeijerG[{{}, {1., 1.}}, {{0., 0., 4.}, {}}, -1.0 T λ]
(* MeijerG[{{}, {1., 1.}}, {{0., 0., 4.}, {}}, -1. T λ] *)
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    $\begingroup$ For a simpler form use MeijerG[{{}, {1., 1.}}, {{0., 0., 4.}, {}}, -1. T \[Lambda]] // Rationalize // FunctionExpand // FullSimplify $\endgroup$
    – Bob Hanlon
    Dec 17, 2015 at 15:08
  • $\begingroup$ Why would you introduce rationalize and Fullsimplify to the expression ? $\endgroup$ Nov 21, 2020 at 6:11

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