index2lm

This IDL routine provides a means to convert the $a_{\ell m}$ index $i = \ell^2 + \ell + m + 1$ (as returned by eg the fits2alm routine) into $\ell$ and m.

Location in HEALPix directory tree: src/idl/misc/index2lm.pro

 

FORMAT

IDL> INDEX2LM, index, l, m

QUALIFIERS

index

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

l

Long array containing on OUTPUT the order $\ell$. It has the same size as index.

m

Long array containing on OUTPUT the degree m. It has the same size as index.

DESCRIPTION

index2lm converts $i = \ell^2 + \ell + m + 1$ into $(\ell, m)$. Note that the index i is only defined for $0 \le \vert m\vert\le \ell$.

RELATED ROUTINES

This section lists the routines related to index2lm

idl

version 6.4 or more is necessary to run index2lm.

fits2alm

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

alm2fits

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

lm2index

routine complementary to index2lm: converts $(\ell, m)$ into $i = \ell^2 + \ell + m + 1$.

EXAMPLE:

index2lm, index, l, m

will return in l and m the order $\ell$ and degree m such that index $=\ell^2 + \ell + m + 1$