# Mehler-Fock transform

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Mehler–Fok transform

 (1)

where is the Legendre function of the first kind (cf. Legendre functions). If , the function is locally integrable on and , then the following inversion formula is valid:

 (2)

The Parseval identity. Consider the Mehler–Fock transform and its inverse defined by the equalities

If , , are arbitrary real-valued functions satisfying the conditions

then

The generalized Mehler–Fock transform and the corresponding inversion formula are:

 (3)

and

 (4)

where are the associated Legendre functions of the first kind. For formulas (3) and (4) reduce to (1) and (2); for , , formulas (3) and (4) lead to the Fourier cosine transform, and for , to the Fourier sine transform. The transforms (1) and (2) were introduced by F.G. Mehler [1]. The basic theorems were proved by V.A. Fock [V.A. Fok].

#### References

 [1] F.G. Mehler, "Ueber eine mit den Kugel- und Cylinderfunctionen verwandte Function und ihre Anwendung in der Theorie der Electricitätsvertheilung" Math. Ann. , 18 (1881) pp. 161–194 [2] V.A. Fok, "On the representation of an arbitrary function by an integral involving Legendre functions with complex index" Dokl. Akad. Nauk SSSR , 39 (1943) pp. 253–256 (In Russian) [3] V.A. Ditkin, A.P. Prudnikov, "Operational calculus" Progress in Math. , 1 (1968) pp. 1–75 Itogi Nauk. Mat. Anal. 1966 (1967) pp. 7–82

#### References

 [a1] I.N. Sneddon, "The use of integral transforms" , McGraw-Hill (1972)
How to Cite This Entry:
Mehler–Fock transform. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Mehler%E2%80%93Fock_transform&oldid=22805