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Goursat's Surface


GoursatsCube
GoursatsSurface

A general quartic surface defined by

 x^4+y^4+z^4+a(x^2+y^2+z^2)^2+b(x^2+y^2+z^2)+c=0
(1)

(Gray 1997, p. 314). The above two images correspond to (a,b,c)=(0,0,-1), and (0,-2,-1), respectively.

Goursat's surface

Additional cases are illustrated above.

The "rounded cube" case corresponding to (a,b,c)=(0,-2,-1) is a superellipsoid with volume

 V(0,-2,-1)=(Gamma^4(1/4))/(6sqrt(2)pi),
(2)

where Gamma(z) is the gamma function.

The volume of the case (a,b,c)=(0,-1,1/2) is given by

V(0,-1,1/2)=4sqrt(2)int_0^1int_(sqrt(1/2-xsqrt(1-x^2)))^(sqrt(1/2+xsqrt(1-x^2)))f(x,y)dydx
(3)
=int_0^infty-(pi^2)/(16sqrt(2))R{((-1)^(5/8))/(t^(7/4))[(-1)^(1/4)e^(it/8)t^(3/4)×[(-1)^(3/4)J_(1/4)(t/8)-J_(-1/4)(t/8)]^3+(12sqrt(t)Gamma(1/4))/(pi^2)+(2(1+i)Gamma^3(1/4))/(pi^3)]}dt
(4)

where

 f(x,y)=sqrt(1+sqrt(4(x^2-x^4+y^2-y^4)-1))-sqrt(1-sqrt(4x^2(1-x^2)-(1-2y^2)^2)),
(5)

R[z] is the real part of z and J_nu(z) is a Bessel function of the first kind (E. W. Weisstein and M. Trott, pers. comm., Nov. 9, 2008), which can probably be expressed in closed form in terms of bivariate hypergeometric functions.

The related surface

 x^n+y^n+z^n=1
(6)

for n>=2 an even integer is also considered by Gray (1997, p. 292) and is a special case of the superellipsoid.


See also

Chmutov Surface, Cube, Superellipsoid, Tooth Surface

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References

Banchoff, T. F. "Computer Graphics Tools for Rendering Algebraic Surfaces and for Geometry of Order." In Geometric Analysis and Computer Graphics: Proceedings of a Workshop Held May 23-25, 1988 (Eds. P. Concus, R. Finn, D. A. Hoffman). New York: Springer-Verlag, pp. 31-37, 1991.Goursat, E. "Étude des surfaces qui admettent tous les plans de symétrie d'un polyèdre régulier." Ann. Sci. École Norm. Sup. 4, 159-2000, 1897.Gray, A. Modern Differential Geometry of Curves and Surfaces with Mathematica, 2nd ed. Boca Raton, FL: CRC Press, pp. 292 and 314, 1997.

Cite this as:

Weisstein, Eric W. "Goursat's Surface." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/GoursatsSurface.html

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