nside2npweights

This IDL facility provides the number pixel-based quadrature weights (in compact non-redundant form) for a given resolution parameter Nside. Because of the HEALPix layout symmetries, $N_w \simeq N_{\mathrm{pix}}/16$, allowing economical storage on disc.

Location in HEALPix directory tree: src/idl/toolkit/nside2npweights.pro 

FORMAT

IDL> Npweights=NSIDE2NPWEIGHTS (Nside [,ERROR=, /HELP])

QUALIFIERS

Nside

HEALPix resolution parameter (integer, scalar or not), should be a valid Nside (power of 2 in $\{1,\ldots,2^{29}\}$)

Npweights

number of non-redundant weights

KEYWORDS

ERROR=

error flag, set to 1 on output if Nside is NOT valid, or stays to 0 otherwise.

/HELP

if set on input, the documentation header is printed out and the routine exits

DESCRIPTION

nside2npweights outputs the number of different pixel-based weights

$$N_w=\frac{(N_{\mathrm{side}}+1)(3N_{\mathrm{side}}+1)}{4}.$$

If the argument N_side is not valid, a warning is issued and the error flag is raised.

RELATED ROUTINES

This section lists the routines related to nside2npweights

idl

version 6.4 or more is necessary to run nside2npweights .

unfold_weights

generates a full sky map of pixel-based or ring-based quadrature weights

EXAMPLE:

Npweights = nside2npweights(256, ERROR=error)

Npweights will be 49408 the number of pixel-based weights for the HEALPix resolution parameter 256 and error will be 0