alm2spec

Evaluate angular power spectral density

Contents

Syntax

cL = alm2spec(alm)
cL = alm2spec(alm, lMax)

Input Arguments

alm real valued coefficients lMax max order of harmonic to calculate (default 20)

Return Arguments

cL      angular power spectrum

Description

The angular power spectrum of the function f,

$$f(\theta,\phi) = \sum a_{\ell m}Y_{\ell m}(\theta,\phi)$$

are the coefficients

$$c_{\ell} = \frac{\sum_{m=-\ell}^\ell |a_{\ell m}|^2}{2*\ell+1}$$

Example

Find power spectrum coefficients of dummy data set

nSide = 2^4;
nPix = nSide2nPix(nSide);
pix = 3*(ylm(nSide,4,2) + ylm(nSide,4,1)) + sqrt(17)*ylm(nSide,8,-4) ...
  + rand(1,nPix);
lMax = 10;
alm = pix2alm(pix,lMax);
cL = alm2spec(alm,lMax);
stem(0:lMax,cL);

See also

pix2alm, alm2pix

Copyright 2010-2011 Lee Samuel Finn. Terms of Use.