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Spheroidal wave functions in MATHEMATICA & system of DE

Posted 10 years ago

Hi, I would like to solve two differential equations using MATHEMATICA. The first equation is:

(1-x^2)*y''[x] - 2*x*y'[x] + (lambda + gamma^2 *(1-x^2))*y[x]=0

where x is a real variable, 0 <= x <=1, and gamma^2 is formally a complex variable having Re{gamma^2} >= 0, but for the purpose of my planned calculations I can assume that gamma^2 is real and nonnegative. Hence, gamma would be real and nonnegative. Parameter lambda is also assumed to be real. The second equation is:

(1+x^2)*y''[x] + 2*x*y'[x] - (lambda + gamma^2 *(1+x^2))*y[x]=0

where x is a real variable, x>=0, and parameters lambda and gamma^2 are the same as in the first equation. The general solutions of the both equations are likely to be expressed by some spheroidal wave functions, which are implemented in MATHEMATICA, although it is not clear which of these functions would occur here. However, function DSolve[] does not recognise the above equations as related to the spheroidal wave functions and does not return any useful solution. Replacement of lambda by SpheroidalEigenvalue[n,0,gamma] does not help. I would appreciate an advice how to use MATHEMATICA to obtain the MATHEMATICA expressions for the general solutions of the above two equations under assumptions stated. Leslaw

POSTED BY: Leslaw Bieniasz
2 Replies
Posted 10 years ago

Yes, but: 1) It is sufficient to omit the term with m^2 and this command will not work. I would argue this is strange and unexpected. 2) The command returns the general solution in terms of SpheroidalPS and SperoidalQS functions only, which is probably correct in the case of the first of my equations, but I need a general solution of the second equation as well. The latter is probably dependent on the functions SpheroidalS1 and SpheroidalS2, but I am unable to guess what should be the correct calling parameters. Why MATHEMATICA does not give the right answer, given the fact that the spheroidal functions are supposed to be implemented? Leslaw

POSTED BY: Leslaw Bieniasz

I don't know anything about spheroidal functions, but in the documentation about SpheroidalPS I see that the differential equation

DSolve[(1 - x^2) y''[x] - 
   2 x y'[x] + (SpheroidalEigenvalue[n, m, c] + c^2 (1 - x^2) - m^2/(
      1 - x^2)) y[x] == 0, y, x]

in solved in terms of Spheroidal functions. Your first equation is similar to the special case with m=0.

POSTED BY: Gianluca Gorni
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