>I am doing some harmonic analysis using the built-in function of fourier_info.
>Also,I know the returned value includes the amplitude and phase of each harmonic.
>But I am wondering what do the amplitude and phase stand for?
> for example:
> f=fourier_info(x,3,1)
> f(0,:,:,:) present the amplitude (amplitude^2= the (real)^2+(imag)^2)
> f(1,:,:,:) present the phase angle
f(2,:,:,:) % variance
> If I want to select wave-1,wave-2,wave-3 and re-build f using the
> fourier_coeficent ,how do I design the script ?
>------------------------------------------------------------------------
AMP(n)*cos(2*pi*n/N + PHASE(n))
AMP : amplitude of harmonic 'n'
PHASE: location of first maximum of AMP
% VAR: relative power
--------------------------------------------
http://www.ncl.ucar.edu/Document/Functions/Built-in/ezfftb.shtml
See Example 3
--------------------------------------------
if X(time,lat,lon)
ab = ezfftf ( X ) ; for all times and latitudes
; ab(2,ntim,nlat,mlon/2)
anot = ab_at_xbar ; mean
;anot = 0.0 ; set all to zero
ab(:,:,:,3:) = 0.0 ; set high coef to 0.0
XX = ezfftb ( ab, anot)
copy_VarMeta(X, XX) ; optional copy meta data
printVarSummary(XX)
Good luck
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Received on Sun Jan 21 2007 - 19:57:25 MST
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