# LOG#235. Hyperballs.

Hi, everyone. The saddest thing about job (working with teenagers and other people) is that it delays other stuff, like blogging! So, you should be patient about getting more of “my stuff”.

What is going on today? Hyperballs. Or hyperspheres and some cool variations. I have written about hyperspheres here before…Even provided formulae for volume (and area) from the. You know, from higher dimensions, as you can get hyperparalletope or cross-polytope with hypervolume , for the known sphere you get and the more general formula for the d hypersphere or usual hyperball volume

(1)

where and . The hyperarea can be obtained from the recurrence in d from lowering dimensions and a useful derivative gadget tool:

(2)

For any 3d ellipsoid you also can derive that, given : , and similar formulae in higher dimensional hyperellipsoids, following the pattern , where is the hypervolume of the unit hypersphere and are the hyperellipsoid (HY) semiaxes.

By the other hand, you do not need to keep things so simple, you can even change the norm in . Thus, having a vector in with norm

then the so-called p-normed hyperball volume in d follows:

In particular, you get y , and those match the expressions for the cross-polytope and the n-cube. Other possible generalization is the next one. For any real positive numbers you can even define the balls:

Since Dirichlet times, mathematicians know the general formula for these hyperballs/hyperspheres:

Enough balls today? Not yet! I wish! I am showing you in a moment why calculus rocks. And not a usual calculus indeed only. Fractional calculus is a variation from common calculus where you can get non-integer derivatives, even irrational, complex or more complicated definitions! Before that, let me remember you as caution that . And know define the Riemann-Liouville operator (fractional derivative):

(3)

Take now . Wow. Then,

(4)

and then, you obtain the partial result

Now, insert with and , then

so, you finally deduce that

(5)

or equivalently

(6)

The fractional recurrence

with holds and note that the general Riemann-Liouville fractional derivative

has gaps or poles, in principle, at values since functions have singularities at negative integers, including zero.

See you in another wonderful blog post!

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