% sky_ng_sim [parameter_file]
A random non-Gaussian white noise map is generated, using either
The resulting map is analyzed into its alm coefficients, which are then multiplied by the beam, pixel and spectrum window
- a simple linear harmonic oscillator, where the PDF of the pixel temperature t is
Hi are the Hermite polynomials, Ci their normalization constants, the variance of the (Gaussian) ground state for are free parameters, while is constrained;
- or, an even power of a gaussian PDF, where the temperature of pixel q is
where g is a zero mean, unit variance Gaussian variable, and P is a user-defined positive integer.
The resulting alm coefficients are turned back into a map, which is therefore non-gaussian, with an effective angular power spectrum (Rocha et al, 2005).
Notes: the code has been modified from the original NGSIMS package in several respects: the seed parameter is named iseed instead of idum, to be consistent with other HEALPix simulation codes; and the SHO generator has been dramatically sped up, without loss of accuracy. Moreover, just like in synfast facility, it is now possible to output the alm coefficients being used (outfile_alms option), and the spatial derivatives of the final map can also be output (simul_type option).
|/data/pixel_window_nxxxx.fits||Files containing pixel windows for various nsmax.|
sky_ng_sim runs in interactive mode, self-explanatory.
When 'filename' is present, sky_ng_sim 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:
sky_ng_sim reads in the Cl power spectrum in 'cl.fits' up to l=256, and produces the map 'map.fits' which has . The non-gaussian white noise was generated assuming a SHO PDF (see Eq 2 above) with and . The map is convolved with a beam of FWHM 30.0 arcminutes. The sets the random seed for the realisation. A different would have given a different realisation from the same power spectrum. And finally, since simul_type= 1 only the map (and not its spatial derivatives) will be output.
were omitted, they take their default values (empty strings). This means respectively that no beam were read, that sky_ng_sim attempts to find the pixel window files in the default directories (see page ), and that the alm generated and used to produce the map were not output.
- Initial release (HEALPix 2.10)
|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.|
Version 3.31, 2017-01-06