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Wrong numerical value

Posted 12 years ago
POSTED BY: M. R.
3 Replies
POSTED BY: Marco Thiel

First I checked the value of

Sqrt[2] Pi^(3/2) / Gamma[1/4]^2

which actually evaluated to:

0.59907

which is not quite what the paper says. I also noticed that the paper is using K and E to denote the complete elliptic integrals of the first and second kind respectively. Unfortunately elliptic integrals can have different notations depending on whose definition is being used. In particular Mathematica (and Abramowitz and Stegun) uses:

$$K (m)=\int _0^{\pi/2}\frac{1}{\sqrt{1-m \sin^2\theta}} d \theta$$

while some others use:

$$K (m)=\int _0^{\pi/2}\frac{1}{\sqrt{1-m^2 \sin^2\theta}} d \theta$$

I assumed that the difference you get is likely due to this, so I tested it (note the squared argument now):

N[Sqrt[2] EllipticE[(1/Sqrt[2])^2] - EllipticK[(1/Sqrt[2])^2]/Sqrt[2]]

which also returns:

0.59907

For clarity of course, I would recommend contacting the authors to determine which definition of the elliptic integrals they used (it would have been nice if they included to reference for it).

POSTED BY: Jesus Hernandez

Sorry for the double posting. I was still typing and did not see that there was already a reply.

M.

POSTED BY: Marco Thiel
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