This routine modifies scalar (and tensor) a_lm 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) $a_{lm} \longrightarrow a_{lm} b(l)$ . It can also be used to multiply the a_lm by an arbitray function of l.

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	${N_{\rm side}}$ resolution parameter of the map associated with the a_lm considered. Currently has no effect on the routine.
nlmax	I4B	IN	maximum l value for the a_lm.
nmmax	I4B	IN	maximum m value for the a_lm.
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_lm 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_l 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_lm. If present, it overrides both `fwhm_arcmin` and `beam_file`. If nlw < nlmax, the a_lm with $l\in \{$ 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_lm of a map with ${N_{\rm side}}=64$ , $l_{\rm max}=m_{\rm max} = 128$ 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_lm coefficients.
rotate_alm: Routine to rotate a_lm coefficients between 2 different arbitrary coordinate systems.
map2alm: Routines to analyze a HEALPix sky map into its a_lm coefficients.
alm2map: Routines to synthetize a HEALPix sky map from its a_lm coefficients.
alms2fits, dump_alms: Routines to save a set of a_lm in a FITS file.

Eric Hivon 2010-06-18

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This routine modifies scalar (and tensor) alm 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) . It can also be used to multiply the alm by an arbitray function of l.

FORMAT

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

ARGUMENTS

EXAMPLE:

MODULES & ROUTINES

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

RELATED ROUTINES

This section lists the routines related to alter_alm*