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alteralm

This program can be used to modify a set of a_lm 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_lm from the input coordinate system to any other standard astrophysical coordinate system. The resulting a_lm 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_lm (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.

(1)

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

FORMAT

% alteralm [options] [parameter_file]

COMMAND LINE OPTIONS

-d

--double

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

-s

--single

single precision mode (default)

QUALIFIERS

infile_alms =

Defines the FITS file from which to read the input a_lm.

outfile_alms =

Defines the FITS file in which to write the altered a_lm.

fwhm_arcmin_in =

Defines the FWHM size in arcminutes of the Gaussian beam present in the input a_lm. The output a_lm will be corrected from it, see Eq. (1). (default= value of FWHM keyword in infile_alms).

beam_file_in =

Defines the FITS file describing the Legendre window function of the circular beam present in the input a_lm. The output a_lm will be corrected from it, see Eq. (1). 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 l value to be used for the output a_lms. (default= maximum l of input a_lm = 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 whose window function is applied to the input a_lm

nsmax_out =

Defines the HEALPix resolution parameter whose window function will be applied to the output a_lm. Could be set to 0 for infinitely small pixels, ie no pixel window function (default= same as input's ).

fwhm_arcmin_out =

Defines the FWHM size in arcminutes of the Gaussian beam to be applied to a_lm, see Eq. (1). (default= fwhm_arcmin_in).

beam_file_out =

Defines the FITS file describing the Legendre window function of the circular beam to be applied a_lm. 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_lm. 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_lm (default = coord_in)

epoch_out =

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

DESCRIPTION

Alteralm can modify temperature as well as polarisation a_lm. It will also modify the error on the a_lm 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.

SUPPORT

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

anafast

This HEALPix Fortran facility can analyse a HEALPix map to extract the a_lm that can be altered by alteralm.

synfast

This HEALPix facility can generate a HEALPix map from a power spectrum C_l, with the possibility of including constraining a_lm as those obtained with alteralm.

EXAMPLE # 1:

Alteralm runs in interactive mode, self-explanatory.

EXAMPLE # 2:

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_lm from 'alm.fits'. Since
nsmax_in
nsmax_out
fwhm_arcmin_in
beam_file_in
coord_in
epoch_in
epoch_out
have their default values, the pixel size will remain the same, the a_lm 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_lm 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

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