This IDL facility provides a means to read from a FITS file an ascii or binary table extension containing power spectrum (C(l)) or spherical harmonics (a_{l m}) coefficients, and returns the corresponding power spectrum ( $C(l) = \sum_m a_{lm}a^*_{lm} / (2l+1)$ ). Reads primary and extension headers if required. The facility is intended to enable the user to read the output from the HEALPix facility anafast.

Location in HEALPix directory tree: src/idl/fits/fits2cl.pro

FORMAT

IDL> FITS2CL, cl_array, fitsfile, [HDR = ,/HELP, /INTERACTIVE, LLFACTOR=, MULTIPOLES=, /RSHOW, /SHOW, /SILENT=, XHDR =]

QUALIFIERS

cl_array: real array of C_l coefficients read or computed from the file. The output dimension depends on the contents of the file. This has dimension either (lmax+1,6) given in the sequence T E B TxE TxB ExB or (lmax+1,4) for T E B TxE or (lmax+1) for T alone. The convention for the power spectrum is that it is not normalised by the Harrison-Zeldovich (flat) spectrum.
fitsfile: String containing the name of the FITS file to be read. The file contains either C(l) power spectra or a_{l m} coefficients. In either cases, C(l) is returned.

KEYWORDS

HDR =: String array containing on output the primary header read from the FITS file.
/HELP: If set, produces an extended help message (using the doc_library IDL command).
/INTERACTIVE: If set, the plots generated by /SHOW and /RSHOW options are produced using iPlot routine, allowing for interactive cropping, zooming and annotation of the plots. This requires IDL 6.4 or newer to work properly.
LLFACTOR =: vector containing on output the factor $l(l+1)/2\pi$ which is often applied to C(l) to flatten it for plotting purposes
MULTIPOLES =: vector containing on output the multipoles l for which the power spectra are provided. They are either
- read from the file (1st column in the Planck format),
- or generated by the routine (assuming that all multipoles from 0 to lmax included are provided).
/RSHOW: If set, the raw power spectra C(l) read from the file are plotted
/SHOW: If set, the rescaled power spectra $l(l+1)C(l)/2\pi$ are plotted
/SILENT: If set, no message is issued during normal execution
XHDR =: String array containing on output the extension header read from the FITS file.

DESCRIPTION

fits2cl reads the power spectrum coefficients from a FITS file containing an ascii table extension. Descriptive headers conforming to the FITS convention can also be read from the input file.

RELATED ROUTINES

This section lists the routines related to fits2cl

idl: version 6.1 or more is necessary to run fits2cl.
bin_llcl: facility to bin a spectrum read with fits2cl.
bl2fits: facility to write a window function into a FITS file.
cl2fits: provides the complimentary routine to write a power spectrum to a FITS file.
fits2alm, alm2fits: routines to read and write a_lm coefficients
ianafast: IDL routine computing C(l) files that can be read by fits2cl.
anafast: F90 facility computing C(l) files that can be read by fits2cl.

EXAMPLE:

fits2cl, pwrsp, '$HEALPIX/test/cl.fits', $

HDR=hdr, XHDR=xhdr, MULTI=l, LLFACT=fll

plot, l, powrsp[*,0]*fll

fits2cl reads a power spectrum C(l) from the input FITS file $HEALPIX/test/cl.fits into the variable pwrsp, with optional headers passed by the string variables hdr and xhdr. The multipoles l and factors $l(l+1)/2\pi$ are read into l and fll respectively. $l(l+1)C(l)/2\pi$ vs l is then plotted.

Eric Hivon 2010-06-18

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