healpy.sphtfunc.synalm¶

healpy.sphtfunc.synalm(cls, lmax=None, mmax=None, new=False, verbose=True)

Generate a set of alm given cl. The cl are given as a float array. Corresponding alm are generated. If lmax is None, it is assumed lmax=cl.size-1 If mmax is None, it is assumed mmax=lmax.

Parameters
clsfloat, array or tuple of arrays

Either one cl (1D array) or a tuple of either 4 cl or of n*(n+1)/2 cl. Some of the cl may be None, implying no cross-correlation. See new parameter.

lmaxint, scalar, optional

The lmax (if None or <0, the largest size-1 of cls)

mmaxint, scalar, optional

The mmax (if None or <0, =lmax)

newbool, optional

If True, use the new ordering of cl’s, ie by diagonal (e.g. TT, EE, BB, TE, EB, TB or TT, EE, BB, TE if 4 cl as input). If False, use the old ordering, ie by row (e.g. TT, TE, TB, EE, EB, BB or TT, TE, EE, BB if 4 cl as input).

Returns
almsarray or list of arrays

the generated alm if one spectrum is given, or a list of n alms (with n(n+1)/2 the number of input cl, or n=3 if there are 4 input cl).

Notes

The order of the spectra will change in a future release. The new= parameter help to make the transition smoother. You can start using the new order by setting new=True. In the next version of healpy, the default will be new=True. This change is done for consistency between the different tools (alm2cl, synfast, anafast). In the new order, the spectra are ordered by diagonal of the correlation matrix. Eg, if fields are T, E, B, the spectra are TT, EE, BB, TE, EB, TB with new=True, and TT, TE, TB, EE, EB, BB if new=False.