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Last data update: 2014.03.03

R: Define a mesh on a unit ball in n-dimensions

UnitSphere

R Documentation

Define a mesh on a unit ball in n-dimensions

Description

Subdivide the unit ball or sphere into approximately equal simplices in arbitrary dimenions.

Usage

UnitSphere(n, k, method = "dyadic", p = 2, positive.only = FALSE)
UnitSphereEdgewise(n, k, p, positive.only)
UnitSphereDyadic(n, k, start = "diamond", p, positive.only)
UnitBall( n, k, method="dyadic", p=2, positive.only=FALSE )
LpNorm(x, p)

Arguments

`n`	Dimension of the space; the unit sphere is an (n-1) dimensional manifold
`k`	Number of subdivisions
`method`	"dyadic" or "edgewise": the former recursively subdivides the sphere to get a more uniform grid; the latter uses a faster method using one edgewise subdivision.
`p`	Power used in the l^p norm; p=2 is the Euclidean norm
`positive.only`	TRUE means restrict to the positive orthant; FALSE gives the full ball
`start`	starting shape: "diamond" or "icosahedron"
`x`	Matrix of points in n-dimensions; each column is a point in R^n

Details

UnitSphere computes a hyperspherical triangle approximation to the unit sphere. It calls either UnitSphereDyadic or UnitSphereEdgewise based on 'method'. Both work by subdividing the first octant, and then rotating that subdivision around to other octants. Note that 'k' has a different meaning for the different methods. When method="dyadic", k specifies the number of dyadic subdivisions. When method="edgewise", k specifies the number of subdivisions as in UnitSimplex, which is then projected outward to the unit sphere. So when n=2, a dyadic subdivision with k=2 will result in 16 edges, whereas an edgewise subdivions with k=2 results in 8 edges.

UnitBall computes an approximate simplicial approximation to the unit ball. Specifically, it generates cones with one vertex at the origin and the other vertices on the surface of the unit sphere; these later vertices are from UnitSphere. If k is large, these cones will be very narrow/thin.

Value

an object of class "mvmesh" as described in mvmesh.

Examples

UnitSphere( n=2, k=2, method="edgewise", positive.only=TRUE )
UnitSphere( n=2, k=2, method="edgewise" )

UnitSphere( n=3, k=2, method="edgewise", positive.only=TRUE )
UnitSphere( n=3, k=2, method="edgewise" )

UnitBall( n=2, k=2, method="edgewise", positive.only=TRUE )
UnitBall( n=2, k=2, method="edgewise" )

UnitSphere( n=3, k=2, method="dyadic", positive.only=TRUE )
UnitSphere( n=3, k=2, method="dyadic" )

UnitBall( n=3, k=2, method="dyadic", positive.only=TRUE )
UnitBall( n=3, k=2, method="dyadic" )

UnitSphere(  n=3, k=2 )
UnitBall( n=3, k=2 )

x <- c(3,-1,2)
LpNorm( x, p=2 )

## Not run: 
plot( UnitSphere(  n=3, k=2 ), show.label=TRUE )
plot( UnitBall( n=3, k=2 ) )


## End(Not run)