DFTreal.py

""" From "COMPUTATIONAL PHYSICS" & "COMPUTER PROBLEMS in PHYSICS"
    by RH Landau, MJ Paez, and CC Bordeianu (deceased)
    Copyright R Landau, Oregon State Unv, MJ Paez, Univ Antioquia, 
    C Bordeianu, Univ Bucharest, 2017. 
    Please respect copyright & acknowledge our work."""

# DFTreal.py:  Discrete Fourier Transform using real numbers

from visual.graph import *

signgr = gdisplay(x=0,y=0,width=600,height=250, \
        title='Signal y(t)= 3 cos(wt)+2 cos(3wt)+ cos(5wt) ',\
	xtitle='x', ytitle='signal',xmax=2.*math.pi,xmin=0,ymax=7,ymin=-7)
sigfig = gcurve(color=color.yellow,display=signgr)
imagr = gdisplay(x=0,y=250,width=600,height=250,\
	    title='Fourier transform imaginary part',xtitle='x',\
        ytitle='Transf.Imag',xmax=10.0,xmin=-1,ymax=20,ymin=-25)
impart = gvbars(delta=0.05,color=color.red,display=imagr)      
 
N = 200                                   
Np = N 
signal = zeros((N+1),float)     
twopi = 2.*pi
sq2pi = 1./sqrt(twopi) 
h = twopi/N
dftimag = zeros((Np),float)                             # Im. transform

def f(signal):                                          
    step = twopi/N
    t= 0. 
    for  i in range(0,N+1):
       signal[i] = 3*sin(t*t*t)  
       sigfig.plot(pos=(t,signal[i]))                      
       t += step
      
def fourier(dftimag):                                            # DFT
    for n in range(0,Np):                                 
      imag = 0.                                         
      for  k in range(0, N):                               
        imag += signal[k]*sin((twopi*k*n)/N) 
      dftimag[n] = -imag*sq2pi                           # Im transform
      if dftimag[n] !=0:                 
          impart.plot(pos=(n,dftimag[n]))                     

f(signal) 
fourier(dftimag)