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Hypercube Point Picking


The expected value B_n(s) of r^s from a fixed vertex of a unit n-cube to a point picked at random in the interior of the hypercube is given by

B_n(s)=int_0^1...int_0^1_()_(n)sqrt(x_1^2+...+x_n^2)dx_1...dx_n
(1)
=s/(Gamma(1-1/2s))int_0^infty(1-[b(u)]^n)/(u^(s+1))
(2)

where r is the distance and

b(u)=int_0^1e^(-u^2x^2)dx
(3)
=(sqrt(pi)erf(u))/(2u)
(4)

(Bailey et al. 2006).

The first few values of expected distances B_n=B_n(1) are given by

B_1=1/2
(5)
B_2=1/3sqrt(2)+1/3ln(sqrt(2)+1)
(6)
B_3=1/4sqrt(3)-1/(24)pi-1/2ln2+ln(1+sqrt(3))
(7)
B_4=2/5+7/(20)pisqrt(2)-1/(20)piln(1+sqrt(2))+ln3-7/5sqrt(2)tan^(-1)(sqrt(2))+1/(10)K_0,
(8)

where the term

K_0=2int_(sqrt(3))^2(ycoth^(-1)y)/(sqrt(y^2-3)(y^2-2))dy
(9)
=2int_0^1(coth^(-1)(sqrt(3+y^2)))/(1+y^2)dy
(10)

is not known in closed form (Bailey et al. 2006; Bailey et al. 2007, pp. 238 and 272).

It is related to the expected distance from the center of the unit n-cube by

 Z_n(s)=(B_n(s))/(2^s)
(11)

(Bailey et al. 2006).


See also

Box Integral, Cube Point Picking, Hypercube Line Picking, Line Point Picking, Square Point Picking

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References

Bailey, D. H.; Borwein, J. M.; and Crandall, R. E. "Box Integrals." Preprint. Apr. 3, 2006.Bailey, D. H.; Borwein, J. M.; Calkin, N. J.; Girgensohn, R.; Luke, D. R.; and Moll, V. H. Experimental Mathematics in Action. Wellesley, MA: A K Peters, 2007.

Referenced on Wolfram|Alpha

Hypercube Point Picking

Cite this as:

Weisstein, Eric W. "Hypercube Point Picking." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/HypercubePointPicking.html

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