alter_alm*

This routine modifies scalar (and tensor) $a_{\ell m}$ by multiplying them by a beam window function described by a FWHM (in the case of a gaussian beam) or read from an external file (in the more general case of a circular beam) $a_{\ell m} \longrightarrow a_{\ell m} b(\ell)$ . It can also be used to multiply the $a_{\ell m}$ by an arbitray function of $\ell$.

Location in HEALPix directory tree: src/f90/mod/alm_tools.F90 

FORMAT

call alter_alm*( nsmax, nlmax, nmmax, fwhm_arcmin, alm_TGC[, beam_file, window] )

ARGUMENTS

name & dimensionality	kind	in/out	description
nsmax	I4B	IN	$N_{\mathrm{side}}$ resolution parameter of the map associated with the $a_{\ell m}$ considered. Currently has no effect on the routine.
nlmax	I4B	IN	maximum $\ell$ value for the $a_{\ell m}$.
nmmax	I4B	IN	maximum $m$ value for the $a_{\ell m}$.
fwhm_arcmin	SP/ DP	IN	fwhm size of the gaussian beam in arcminutes.
alm_TGC(1:p,0:nlmax,0:nmmax)	SPC/ DPC	INOUT	complex $a_{\ell m}$ values to be altered. The first index here runs from 1:1 for temperature only, and 1:3 for polarisation. In the latter case, 1=T, 2=E, 3=B.

beam_file(LEN=filenamelen) (OPTIONAL)	CHR	IN	name of the file containing the (non necessarily gaussian) window function $B_\ell$ of a circular beam. If present, it will override the argument fwhm_arcmin.
window(0:nlw,1:d) (OPTIONAL)	SP/ DP	IN	arbitrary window by which to multiply the $a_{\ell m}$. If present, it overrides both fwhm_arcmin and beam_file. If nlw $<$ nlmax, the $a_{\ell m}$ with $\ell \in \{$nlw+1,nlmax$\}$ are set to 0, and a warning is issued. If $d<p$ the window for temperature is replicated for polarisation.

EXAMPLE:

call alter_alm(64, 128, 128, 1, 5.0, alm_TGC)

Alters scalar and tensor $a_{\ell m}$ of a map with $N_{\mathrm{side}}=64$, $\ell_{\mathrm{max}}=m_{\mathrm{max}}= 128$ by multiplying them by the beam window function of a gaussian beam with FWHM = 5 arcmin.

MODULES & ROUTINES

This section lists the modules and routines used by alter_alm*.

alm_tools

module, containing:

generate_beam

routine to generate beam window function

pixel_window

routine to generate pixel window function

RELATED ROUTINES

This section lists the routines related to alter_alm*

create_alm

Routine to create $a_{\ell m}$ coefficients.

rotate_alm

Routine to rotate $a_{\ell m}$ coefficients between 2 different arbitrary coordinate systems.

map2alm

Routines to analyze a HEALPix sky map into its $a_{\ell m}$ coefficients.

alm2map

Routines to synthetize a HEALPix sky map from its $a_{\ell m}$ coefficients.

alms2fits, dump_alms

Routines to save a set of $a_{\ell m}$ in a FITS file.