rect2polar: n-dimensional polar coordinate transformations

In SphericalCubature: Numerical Integration over Spheres and Balls in n-Dimensions; Multivariate Polar Coordinates

Description

Convert between polar and rectangular coordinates in n-dimensions. The point (x[1],...,x[n]) in rectangular coordinates corresponds to the point (r,phi[1],...,phi[n-1]) in polar coordinates.

Usage

polar2rect(r, phi)
rect2polar(x)

Arguments

r	a vector of radii of length m.
phi	angles, a matrix of size (n-1) x m.
x	(n x m) matrix, with column j being the point in n-dimensional space.

Details

n dimensional polar coordinates are given by the following:
rectangular x=(x[1],...,x[n]) corresponds to polar (r,phi[1],...,phi[n-1]) by
x[1] = r*cos(phi[1])
x[j] = r*prod(sin(phi[1:(j-1)]))*cos(phi[j]), 2 <= j <= n-1
...
x[n] = r*sin(phi[1])*sin(phi[2])*...*sin(phi[n-2])*sin(phi[n-1])

This is the defintion used in Wikipedia under the topic 'n-sphere'. There are variations of this definition in use. Here phi[1],...,phi[n-2] are in [0,pi), and phi[n-1] is in [0,2*pi). For multivariate integration, the determinant of the Jacobian of the above tranformation is J(r,phi) = r^(n-1) * prod( sin(phi[1:(n-2)])^((n-2):1) ); note that phi[n-1] does not appear in the Jacobian.

Value

For polar2rect( ), an (n x m) matrix of rectangular coordinates.

For rect2polar( ), a list with fields:

r	a vector of length m containing the radii
phi	angles, a matrix of size (n x m)

Examples

x <- matrix( 1:9, nrow=3 )
x
a <- rect2polar( x )
a
polar2rect( a$r, a$phi )

Example output

Loading required package: cubature
Loading required package: SimplicialCubature
Loading required package: mvmesh
Loading required package: rcdd
If you want correct answers, use rational arithmetic.
See the Warnings sections added to help pages for
    functions that do computational geometry.

Loading required package: rgl
Loading required package: geometry
Loading required package: abind
Warning messages:
1: In rgl.init(initValue, onlyNULL) : RGL: unable to open X11 display
2: 'rgl_init' failed, running with rgl.useNULL = TRUE 
3: .onUnload failed in unloadNamespace() for 'rgl', details:
  call: fun(...)
  error: object 'rgl_quit' not found 
     [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9
$r
[1]  3.741657  8.774964 13.928388

$phi
          [,1]      [,2]     [,3]
[1,] 1.3002466 1.0974780 1.044227
[2,] 0.9827937 0.8760581 0.844154

     [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9

SphericalCubature documentation built on Jan. 13, 2021, 1:04 p.m.