ialteralm

This IDL facility provides an interface to F90 'alteralm' facility. This program can be used to modify a set of $a_{\ell m}$ spherical harmonics coefficients, as those extracted by ianafast or simulated by isynfast, before they are used as constraints on a isynfast run. Currently the alterations possible are

• rotation (using Wigner matrices) of the $a_{\ell m}$ from the input coordinate system to any other standard astrophysical coordinate system. The resulting $a_{\ell m}$ can be used with e.g. synfast to generate a map in the new coordinate system.
• removal of the pixel and beam window functions of the input $a_{\ell m}$ (corresponding to the pixel size and beam shape of the map from which they were extracted) and implementation of an arbitrary pixel and beam window function.
  

  $$a_{\ell m}^\mathrm{OUT} = a_{\ell m}^\mathrm{IN} \frac{B^\mathrm{OUT}(\ell) P^\mathrm{OUT}(\ell)}{B^\mathrm{IN}(\ell) P^\mathrm{IN}(\ell)},$$ (6)

  
  
  where $P(\ell)$ is the pixel window function, and $B(\ell)$ is the beam window function (assuming a circular beam) or any other $\ell$ space filter (eg, Wiener filter). For an infinitely small pixel (or beam) one would have $P(\ell) = 1$ (resp. $B(\ell) = 1$) for any $\ell$.

Location in HEALPix directory tree: src/idl/interfaces/ialteralm.pro 

FORMAT

IDL> IALTERALM, alm_in, alm_out, [ beam_file_in, beam_file_out, binpath=, coord_in, coord_out, epoch_in, epoch_out, fwhm_arcmin_in, fwhm_arcmin_out, /help, keep_tmp_files=, lmax_out, nlmax_out, nside_in, nside_out, nsmax_in, nsmax_out, /silent, tmpdir=, windowfile_in, winfiledir_in, windowfile_out, winfiledir_out ]

QUALIFIERS

alm_in

required input: input $a_{\ell m}$, must be a FITS file

alm_out

required output: output $a_{\ell m}$, must be a FITS file

KEYWORDS

binpath=

full path to back-end routine default:$HEXE/alteralm, then $HEALPIX/bin/alteralm
– a binpath starting with / (or $\backslash$),   or $ is interpreted as absolute
– a binpath starting with ./ is interpreted as relative to current directory
– all other binpaths are relative to $HEALPIX

beam_file_in=

Beam window function of input $a_{\ell m}$, either a FITS file or an array (see ”Beam window function files” section in the HEALPix Fortran Facilities document). If present, will override fwhm_arcmin_in default:value of BEAM_LEG keyword read from alm_in

beam_file_out=

Beam window function of output alm, either a FITS file or an array (see beam_file_in. If present and non-empty, will override fwhm_arcmin_out default:” (empty string, no beam window applied)

coord_in=

Astrophysical coordinates system used to compute input $a_{\ell m}$. Case-insensitive single letter code. Valid choices are 'g','G' = Galactic, 'e','E' = Ecliptic, 'c','q','C','Q' = Celestial/eQuatorial. default:value of COORDSYS keyword read from alm_in

coord_out=

Astrophysical coordinates system of output alm. default: coord_in

epoch_in=

Astronomical epoch of input coordinates (coord_in) default:2000.0

epoch_out=

Astronomical epoch of output coordinates (coord_out) default:same as epoch_in

fwhm_arcmin_in=

Full Width Half-Maximum in arcmin of Gaussian beam applied to map from which are obtained input $a_{\ell m}$.
default:value of FWHM keyword in alm_in

fwhm_arcmin_out=

FWHM in arcmin to be applied to output alm.
default:fwhm_arcmin_in

/help

if set, prints extended help

/keep_tmp_files

if set, temporary files are not discarded at the end of the run

lmax_out=, nlmax_out=

maximum multipole of output alm

nside_in=, nsmax_in=

HEALPix resolution parameter of map from which were computed input $a_{\ell m}$ default:determined from alm_in

nside_out=,nsmax_out=

HEALPix resolution parameter Nside whose window function will be applied to output alm.
Could be set to 0 for infinitely small pixels (no window) default:same as input nsmax_in

/silent

if set, works silently

tmpdir=

directory in which are written temporary files default:IDL_TMPDIR (see IDL documentation)

windowfile_in=

FITS file containing pixel window for nside_in default:determined automatically by back-end routine. Do not set this keyword unless you really know what you are doing

winfiledir_in=

directory where windowfile_in is to be found default:determined automatically by back-end routine. Do not set this keyword unless you really know what you are doing

windowfile_out=

FITS file containing pixel window for nside_out default:determined automatically by back-end routine. Do not set this keyword unless you really know what you are doing

winfiledir_out=

directory where windowfile_out is to be found default:determined automatically by back-end routine. Do not set this keyword unless you really know what you are doing

DESCRIPTION

ialteralm is an interface to 'alteralm' F90 facility. It requires some disk space on which to write the parameter file and the other temporary files. Most data can be provided/generated as an external FITS file, or as a memory array.

RELATED ROUTINES

This section lists the routines related to ialteralm

idl

version 6.4 or more is necessary to run ialteralm.

alteralm

F90 facility called by ialteralm.

ianafast

IDL Interface to F90 anafast and C++ anafast_cxx

iprocess_mask

IDL Interface to F90 process_mask

ismoothing

IDL Interface to F90 smoothing

isynfast

IDL Interface to F90 synfast

EXAMPLE:

ialteralm, !healpix.path.test+'alm.fits', '/tmp/alm_equat.fits', $

coord_in='g',coord_out='q'

isynfast, 0, alm_in='/tmp/alm_equat.fits', '/tmp/map_equat.fits'

mollview,'/tmp/map_equat.fits',1

mollview,'/tmp/map_equat.fits',2

This example script reads the test (polarised) $a_{\ell m}$ located in $HEALPIX/test/alm.fits and rotates them from Galactic to Equatorial coordinates, it then synthetizes a map out of those, and finally plots its I and Q Stokes components (in Equatorial coordinates)