# healpy.sphtfunc.alm2cl¶

healpy.sphtfunc.alm2cl(alms1, alms2=None, lmax=None, mmax=None, lmax_out=None, nspec=None)

Computes (cross-)spectra from alm(s). If alm2 is given, cross-spectra between alm and alm2 are computed. If alm (and alm2 if provided) contains n alm, then n(n+1)/2 auto and cross-spectra are returned.

Parameters
almcomplex, array or sequence of arrays

The alm from which to compute the power spectrum. If n>=2 arrays are given, computes both auto- and cross-spectra.

alms2complex, array or sequence of 3 arrays, optional

If provided, computes cross-spectra between alm and alm2. Default: alm2=alm, so auto-spectra are computed.

lmaxNone or int, optional

The maximum l of the input alm. Default: computed from size of alm and mmax_in

mmaxNone or int, optional

The maximum m of the input alm. Default: assume mmax_in = lmax_in

lmax_outNone or int, optional

The maximum l of the returned spectra. By default: the lmax of the given alm(s).

nspecNone or int, optional

The number of spectra to return. None means all, otherwise returns cl[:nspec]

Returns
clarray or tuple of n(n+1)/2 arrays

the spectrum <alm x alm2> if alm (and alm2) is one alm, or the auto- and cross-spectra <alm*[i] x *alm2*[j]> if alm (and alm2) contains more than one spectra. If more than one spectrum is returned, they are ordered by diagonal. For example, if *alm is almT, almE, almB, then the returned spectra are: TT, EE, BB, TE, EB, TB.