Looman–Menchoff theorem

Looman–Menchoff theorem

In the mathematical field of complex analysis, the Looman–Menchoff theorem states that a continuous complex-valued function defined in an open set of the complex plane is holomorphic if and only if it satisfies the Cauchy-Riemann equations. It is thus a generalization of Goursat's theorem, which in addition to assuming the continuity of "f", also supposes its Fréchet differentiability when regarded as a function from a subset of R2 to R2.

A complete statement of the theorem is as follows:

* Let Ω be an open set in C and "f" : Ω → C a continuous function. Suppose that the partial derivatives partial f/partial x and partial f/partial y exist everywhere in Ω. Then "f" is holomorphic if and only if it satisfies the Cauchy-Riemann equation:::frac{partial f}{partialar{z = frac{1}{2}left(frac{partial f}{partial x} + ifrac{partial f}{partial y} ight)=0.

References

*citation|title=When is a Function that Satisfies the Cauchy-Riemann Equations Analytic?|first1=J. D.|last1=Gray|first2=S. A.|last2=Morris|journal=The American Mathematical Monthly|volume=85|number=4|year=1978|publication-date=April 1978|pages=246–256|url=http://www.jstor.org/stable/2321164|doi=10.2307/2321164.
*citation|first=H.|last=Looman|title=Über die Cauchy-Riemannschen Differentialgleichungen|journal=Göttinger Nach.|year=1923|pages=97–108.
*citation|first=D.|last=Menchoff|title=Les conditions de monogénéité|publication-place=Paris|year=1936.
*citation|first=P.|last=Montel|title=Sur les différentielles totales et les fonctions monogènes|journal=C. R. Acad. Sci. Paris|volume=156|uear=1913|pages=1820–1822.
*citation|first=Raghavan|last=Narasimhan|title=Complex Analysis in One Variable|url=http://books.google.com/books?id=J-J4HmIDnOwC&pg=PA43&lpg=PA43&dq=%22Looman-Menchoff+theorem%22&source=web&ots=bBhleDsqtM&sig=Z2P6e4oBxpZDJeTqQAnXvsI6hr0&hl=en#PPA49,M1|year=2001|publisher=Birkhäuser|isbn=0817641645.


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