[ncl-talk] a classic (slow) Fourier transform function

[Md. Jalal Uddin]

Hi all,

The following Fourier Transformation Function gives me constant 0 value. Is
there anyone who can guide me to solve this issue?

undef ("fftwavenumber")
function fftwavenumber (in[*]:numeric)

local in,p,a,b,f,output

begin
    N=dimsizes(in)

   if mod(N,2).eq.0 then
         p=N/2     ; N even
   else
         p=(N-1)/2 ; N odd
   end if

pi=3.1416

a = new((/ p /), typeof(in),getVarFillValue(in))
b = new((/ p /), typeof(in),getVarFillValue(in))

do k=0,p-1
  do t=0,N-1
      a(k) = (2/N)*( in(t)*cos(2*pi*k*t/N) )
      b(k) = (2/N)*( in(t)*sin(2*pi*k*t/N) )
  end do
end do

f = new((/ k,t /), typeof(in),getVarFillValue(in))
output = new((/ t /), typeof(in),getVarFillValue(in))

do t=0,N-1
   do k=0,p-1
        f(k,t) = a(k)*cos(2*pi*k*t/N)+ b(k)*sin(2*pi*k*t/N)
   end do
   output(t)=(sum(f(0,t)))  ; 0 used for Fourier Decomposition (wave number
1)
   return(output)
end do
end


-- 
*Md. Jalal Uddin*
MSc in Applied Meteorology
Nanjing University of Information, Science and Technology, China
B.Sc. in Disaster Management (Hons.)
Patuakhali Science and Technology University, Bangladesh.
Cell: +8613260859092, +8801792052662
Web: www.dmjalal90.weebly.com
Facebook: jalal.hossen.39
LinkedIn: https://bd.linkedin.com/in/md-jalal-uddin-80a026b0
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