alteralm

This program can be used to modify a set of $a_{\ell m}$ spherical harmonics coefficients, as those extracted by anafast or simulated by synfast, before they are used as constraints on a synfast 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.
  

  $$a_{\ell m}^\mathrm{OUT} = a_{\ell m}^\mathrm{IN} \frac{B^\mathrm{OUT}(\ell) P^\mathrm{OUT}(\ell)}{B^\mathrm{IN}(\ell) P^\mathrm{IN}(\ell)},$$ (3)

  
  
  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/f90/alteralm/alteralm.f90 

FORMAT

% alteralm [options] [parameter_file]

COMMAND LINE OPTIONS

-d

--double

double precision mode (see Notes on double/single precision modes)

-s

--single

single precision mode (default)

QUALIFIERS

infile_alms =

Defines the FITS file from which to read the input $a_{\ell m}$.

outfile_alms =

Defines the FITS file in which to write the altered $a_{\ell m}$.

fwhm_arcmin_in =

Defines the FWHM size in arcminutes of the Gaussian beam present in the input $a_{\ell m}$. The output $a_{\ell m}$ will be corrected from it, see Eq. (3). (default= value of FWHM keyword in infile_alms).

beam_file_in =

Defines the FITS file (see ”Beam window function files” in introduction) describing the Legendre window function of the circular beam present in the input $a_{\ell m}$. The output $a_{\ell m}$ will be corrected from it, see Eq. (3). If set to an existing file name, it will override the fhwm_arcmin_in given above. (default= value of the BEAM_LEG keyword in infile_alms)

nlmax_out =

Defines the maximum $\ell$ value to be used for the output $a_{\ell m}$s. (default= maximum $\ell$ of input $a_{\ell m}$ = value of MAX-LPOL keyword in infile_alms).

nsmax_in =

If it can not be determined from the input file infile_alms, asks for the HEALPix resolution parameter N_side whose window function is applied to the input $a_{\ell m}$

nsmax_out =

Defines the HEALPix resolution parameter N_side whose window function will be applied to the output $a_{\ell m}$. Could be set to 0 for infinitely small pixels, ie no pixel window function (default= same as input's N_side).

fwhm_arcmin_out =

Defines the FWHM size in arcminutes of the Gaussian beam to be applied to $a_{\ell m}$, see Eq. (3). (default= fwhm_arcmin_in).

beam_file_out =

Defines the FITS file (see ”Beam window function files” in introduction) describing the Legendre window function of the circular beam to be applied $a_{\ell m}$. If set to an existing file name, it will override the fhwm_arcmin_out given above. (default= ” ”)

coord_in =

Defines astrophysical coordinates used to compute the input $a_{\ell m}$. Valid choices are 'G' = Galactic, 'E' = Ecliptic, 'C'/'Q' = Celestial = eQuatorial. (default = value of COORDSYS keyword read from input FITS file)

epoch_in =

Defines astronomical epoch of input coordinate system (default=2000)

coord_out =

Defines astrophysical coordinates into which to rotate the $a_{\ell m}$ (default = coord_in)

epoch_out =

Defines astronomical epoch of output coordinate system (default=epoch_in)

windowfile_in =

Defines the input filename from which to read the pixel window function parameterized by nsmax_in (default= pixel_window_n????.fits, see Notes on default files and directories)

winfiledir_in =

Defines the directory in which windowfile_in is located (default : see above).

windowfile_out =

Defines the input filename from which to read the pixel window function parameterized by nsmax_out (default= pixel_window_n????.fits, see above)

winfiledir_out =

Defines the directory in which windowfile_out is located (default : see above).

DESCRIPTION

Alteralm can modify temperature as well as polarisation $a_{\ell m}$. It will also modify the error on the $a_{\ell m}$ if those are provided. It works best if the input FITS file contains the relevant information on the beam size and shape, maximum multipoles, ...

DATASETS

The following datasets are involved in the alteralm processing.

Dataset	Description
/data/pixel_window_nxxxx.fits	Files containing pixel windows for various nsmax.

SUPPORT

This section lists those routines and facilities (including those external to the HEALPix distribution) which can assist in the utilisation of alteralm.

generate_beam

This HEALPix Fortran subroutine generates or reads the $B(\ell)$ window function(s) used in alteralm

anafast

This HEALPix Fortran facility can analyse a HEALPix map to extract the $a_{\ell m}$ that can be altered by alteralm.

synfast

This HEALPix facility can generate a HEALPix map from a power spectrum $C_\ell$, with the possibility of including constraining $a_{\ell m}$ as those obtained with alteralm.

EXAMPLE # 1:

alteralm

Alteralm runs in interactive mode, self-explanatory.

EXAMPLE # 2:

alteralm filename

When 'filename' is present, alteralm enters the non-interactive mode and parses its inputs from the file 'filename'. This has the following structure: the first entry is a qualifier which announces to the parser which input immediately follows. If this input is omitted in the input file, the parser assumes the default value. If the equality sign is omitted, then the parser ignores the entry. In this way comments may also be included in the file. In this example, the file contains the following qualifiers:
infile_alms= alm.fits
nlmax_out= 512
fwhm_arcmin_out= 20.0
coord_out= G
outfile_alms= newalm.fits

Alteralm reads the $a_{\ell m}$ from 'alm.fits'. Since
nsmax_in
nsmax_out
fwhm_arcmin_in
beam_file_in
coord_in
epoch_in
epoch_out
windowfile_in
winfiledir_in
windowfile_out
winfiledir_out
have their default values, the pixel size will remain the same, the $a_{\ell m}$ will be corrected from its input beam (whatever it was, assuming the relevant information can be found), and a gaussian beam of 20.0 arcmin will be applied instead, the $a_{\ell m}$ will also be rotated from their original coordinate system (whatever it was, assuming the relevant information can be found) into Galactic coordinates, assuming a year 2000 epoch for both, and only the multipoles up to 512 will be written in 'newalm.fits'.

RELEASE NOTES

■ Initial release (HEALPix 2.00)

MESSAGES

This section describes error messages generated by alteralm

Message	Severity	Text
can not allocate memory for array xxx	Fatal	You do not have sufficient system resources to run this facility at the map resolution you required. Try a lower map resolution.
this is not a binary table		the fitsfile you have specified is not of the proper format
there are undefined values in the table!		the fitsfile you have specified is not of the proper format
the header in xxx is too long		the fitsfile you have specified is not of the proper format
XXX-keyword not found		the fitsfile you have specified is not of the proper format
found xxx in the file, expected:yyyy		the specified fitsfile does not contain the proper amount of data.
alteralm> no information found on input alms beam	Fatal	no information on the input beam was found, neither from parsing the FITS file header, nor from what the user provided.