# How to get an expression for a Hypergeometric function with symbiotic variable

2 vues (au cours des 30 derniers jours)
Drawing le 9 Avr 2024
Commenté : Drawing le 11 Avr 2024
I want to calculate the inverse Laplace transform of ,
where G(r)= , s is the variable.
My code can't compute a Hypergeometric function function with symbolic variable, and it can't get a concrete inverse Laplace transformation.
here is my code
phi=4;alpha=2.2;beta=4.7e-05;rho=25;r1=500;r2=400;lambda=4.0e-05;
syms s r t
G_r=0.5*r^2*(hypergeom([phi,-2/alpha],(alpha-2)/alpha,-r^(-alpha)*beta*rho*s )-1);
L_IBd00_s=exp(2*pi*lambda*( vpa(subs(G_r,r,r1),5) -vpa(subs(G_r,r,r2),5) ));
L_IBd00_inv=ilaplace(1/s*L_IBd00_s);
the result is
ans =
125000.0*hypergeom([-0.90909, 4.0], 0.090909, -1.342e-9*s) - 125000.0
>> vpa(L_IBd00_inv,5)
ans =
0.000012253*heaviside(t)*ilaplace(exp(10.0*pi*hypergeom([-0.90909, 4.0], 0.090909, -1.342e-9*s) - 6.4*pi*hypergeom([-0.90909, 4.0], 0.090909, -2.1926e-9*s))/s, s, t)
So how can i get an expression of L_IBd00_inv with respect to the variable t?
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### Réponse acceptée

Torsten le 9 Avr 2024
Déplacé(e) : Torsten le 9 Avr 2024
MATLAB is not able to find the Inverse Laplace transform of such a complicated function as an analytic expression.
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Torsten le 10 Avr 2024
What kind of simplified representation of 125000.0*hypergeom([-0.90909, 4.0], 0.090909, -1.342e-9*s) - 125000.0 do you expect to get ? "hypergeom" is defined by an infinite series expression. Do you think this will be easier to handle for "ilaplace" ?
Drawing le 11 Avr 2024
Hello, Torsten! I thought i can get a simplified representation like " hypergeom([4.2,-1],2.2,1.1*s ) ans =1 - (21*s)/10", so that this will be easier to handle for "ilaplace" .
I read this opinion from a paper, the author mentioned "the inverse Laplace transform of 1/s*" can be computed directly in MATLAB.

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