The observable
quantity *f* is fitted as

f(r,theta) = sum_{cmi..}{A(r)cos(cmi*theta) + sum_{smi..}{B(r)sin(smi*theta)where

can be any arbitrary

Optionally the cos (A) and sin (B) coefficients can
be transformed into an amplitude (C) and phase (P), see **amode=** below.

**in=***in_file*- Input data file, must be in standard
*snapshot(5NEMO)*format [No default]. **radii=***rmin,r1,..,rmax*- Radii of the rings (but see
**xvar**and**yvar**below) within which the fourier coefficients are computed. [Default:**0:2:0.2**]. **cos=***cm1,cm2,..*- Set of integers for which the cosine amplitudes need
to be computed. [Default:
**0:4**]. **sin=***sm1,sm2,..*- Set of integers for which the
sine amplitudes need to be computed. [Default:
**1:4**]. **xvar=***x-variable*- X-variable
which is used to compute the radius and angle used in the fourier decomposition.
[Default:
**x**]. **yvar=***y-variable*- Y-variable which is used to compute the radius
and angle used in the fourier decomposition. [Default:
**y**]. **fvar=***f-variable*- Fourier-variable which is the variable used in in the fourier decomposition.
[Default:
**vy**]. **weight=***w-variable*- Weight-variable which is the weight applied
to the observable. [Default:
**1**]. **amode=t|f**- Logical; if true it displays the
sin and cos terms, if false, the amplitudes and phases (in degrees). [Default:
**t**] **times=***t1,t2,...*- Times to select for analysis. [Default:
**all**].

% mkexpdisk disk1 10000 % snapfour disk1 amode=f > tab1 % tabplot tab1 1 4,3,6,8,10 line=1,1 color=2,3,4,5 ycoord=0 % tabplot tab1 1 5:11:2 line=1,1 color=2,3,4,5 ycoord=0Another case is that of an inclined disk that first needs to be rectified, but preserving the position angle of the major axis. Lets assume the

% snaprotate disk1 disk2 theta=-$pa,-$inc,$pa order=zyz % snapfour disk2 ...and for the latter case

% snaprotate disk1 - theta=-$pa order=z |\ snapscale - - rscale="1/cosd($inc),1,0" |\ snaprotate - disk2 theta=$pa order=z % snapfour disk2 ...

Binney, J.J. & Spergel, D. (1982) ApJ 253, 308.

~/src/nbody/reducsnapfour.c

3-dec-90V1.0: writtenPJT 17-feb-92V1.1: added weight=PJT 10-nov-93V1.2: added times=pjt