lm2index

This IDL routine provides a means to convert the $a_{\ell m}$ degree and order $(\ell, m)$ into the index $i = \ell^2 + \ell + m + 1$ (in order to be fed to alm2fits routine for instance)

Location in HEALPix directory tree: src/idl/misc/lm2index.pro

 

FORMAT

IDL> LM2INDEX, l, m, index

QUALIFIERS

l

Long array containing on INPUT the order $\ell$.

m

Long array containing on INPUT the degree m.

index

Long array containing on OUTPUT the index
$i = \ell^2 + \ell + m + 1$.

DESCRIPTION

lm2index converts $(\ell, m)$ into $i = \ell^2 + \ell + m + 1$. Note that by definition $0 \le \vert m\vert\le \ell$ (the routine does not check for this).

RELATED ROUTINES

This section lists the routines related to lm2index

idl

version 6.4 or more is necessary to run lm2index.

fits2alm

reads a FITS file containing $a_{\ell m}$ values.

alm2fits

writes $a_{\ell m}$ values into a FITS file.

index2lm

routine complementary to lm2index: converts $i = \ell^2 + \ell + m + 1$ into $(\ell, m)$.

EXAMPLE:

lm2index, l, m, index

will return in index the value $\ell^2 + \ell + m + 1$