An even Mathieu function with characteristic value .
Elliptic Cosine
See also
Elliptic Sine, Mathieu FunctionExplore with Wolfram|Alpha
References
Frenkel, D. and Portugal, R. "Algebraic Methods to Compute Mathieu Functions." J. Phys. A: Math. Gen. 34, 3541-3551, 2001.Referenced on Wolfram|Alpha
Elliptic CosineCite this as:
Weisstein, Eric W. "Elliptic Cosine." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/EllipticCosine.html