This IDL function turns an indexed list of alm (as generated by fits2alm) into a tabular (real or complex) a(l,m) array for easier manipulation

Location in HEALPix directory tree: src/idl/misc/ 


IDL> alm_table=alm_i2t(Index, Alm_vec, [/COMPLEX, /HELP, LMAX=, MMAX=])


Integer vector of size ni containing the index i of the of alm coefficients, related to {l,m} by i = l2 + l + m + 1
Array of alm coefficients, with dimension (ni, nalm [,nsig]) where
ni = number of i indices
nalm = 2 for real and imaginary parts of alm coefficients or
4 for above plus corresponding error values
nsig = number of signals (usually 1 for any of T E B or 3 for T,E,B together)


if set, the output array is complex with dimensions (lmax+1, mmax+1, [nalm/2 , nsig]),
otherwise, the array is real with dimensions (lmax+1, mmax+1, nalm [, nsig]).
lmax and mmax are determined from input Index values, unless set otherwise by user.
if set, prints out the help header and exits
lmax to be used in output array, regardless of value found in input index
mmax to be used in output array, regardless of value found in input index


alm_i2t returns a real or complex array, containing the alm with $0 \le l \le l_{\rm max}$ and $0 \le m \le m_{\rm max}$. The negative m are therefore ignored.


This section lists the routines related to alm_i2t

version 6.4 or more is necessary to run alm_i2t.
turns tabular alm's such as those generated by alm_i2t into indexed lists than can written to FITS files with alm2fits
alm2fits, fits2alm
routines to read and write alm indexed lists from and to FITS files.


fits2alm, i1, a1, 'alm1.fits'
ac1 = alm_i2t(i1, a1, /complex, lmax=100, mmax=100)
fits2alm, i2, a2, 'alm2.fits'
ac2 = alm_i2t(i2, a2, /complex, lmax=100, mmax=100)
ac = 0.9*ac1 + 0.1*ac2
alm_t2i, ac, i, a
alm2fits, i, a, 'almsum.fits'
The example above reads 2 sets of alm from FITS files, puts the alm's with (l,m) $\le 100$ in tabular arrays, and then make a weighted sum of the alm's. The resulting alm or put back into a indexed list in order to be written to FITS.

Version 3.31, 2017-01-06