ring_analysis


This subroutine computes the Fast Fourier Transform of a single ring of pixels and extends the computed coefficients up to the maximum m of the transform.

Location in HEALPix directory tree: src/f90/mod/alm_tools.F90 


FORMAT

call ring_analysis( nsmax, nlmax, nmmax, datain, nph, dataout, kphi0 )


ARGUMENTS

name & dimensionality kind in/out description
       
nsmax I4B IN ${N_{\rm side}}$ of the map.
nlmax I4B IN Maximum l of the analysis.
nmmax I4B IN Maximum m of the analysis.
nph I4B IN The number of points on the ring.
datain(0:nph-1) DP IN Function values on the ring.
dataout(0:nmmax) DPC OUT Fourier components, replicated to Nmmax.
kphi0 I4B IN 0 if the first pixel on the ring is at $\phi=0$; 1 otherwise.


EXAMPLE:

call ring_analysis(64,128,128,datain,8,dataout,0)
Returns the periodically extended complex Fourier Transform of datain in dataout. They are returned in the following order: 0 1 2 3 4 5 6 7 6 5 4 3 2 1 $0\dots$. The value kphi0=0 specifies that no phase factor needed to be applied, because the ring starts at $\phi=0$.


MODULES & ROUTINES

This section lists the modules and routines used by ring_analysis.

healpix_fft
module.


RELATED ROUTINES

This section lists the routines related to ring_analysis

ring_synthesis
Inverse transform (complex-to-real), used in alm2map, alm2map_der and synfast

Version 3.31, 2017-01-06