from pylab import *
from rectangular import *

def  fra (z,wl):

    dxi = 0.1
    xi = arange(-10,10,dxi)
    a = (len(xi)/2)
    m = arange(-a,a)
    M = len(m)
    wx = 5

    U1 = rect(xi/(2*wx))/(2*wx)
    
    ## plot function
    subplot(2,2,1)
    plot(xi,U1)

    ft = fftshift(fft(U1))
    
    ## plot fourier transform
    subplot(2,2,2)
    plot (xi,ft)

    k = (2*pi)/wl
    p = m
    dx = (wl*z)/(dxi*M)
    x = p*dx

    ##phase calculation
    pIs = exp(1j*z*k)/(1j*wl*z)
    pDs = exp((1j*k*(x**2))/(2*z))

    U2 = pIs*pDs*ft

    ##Brake down of insensity calculation
    A = 2*wx
    b = wl*z
    
    I = (((A/b))*(sinc((A*x)/b)))**2

    subplot(2,2,3)
    plot (x,I)
    
    ## plot calculated Intensity and Intensity
    subplot(2,2,4)
    plot (x,U2*U2.conj())
    #plot (x,I)