Advanced plotting

Consider the following problem:

Display the 2D Fourier transform intensity of a square slit.

(The 2D Fourier transform intensity is the diffraction pattern). Enter the following into square_fft.m :

echo on

 colormap(hsv);

 x=zeros(32);

 x(13:20,13:20)=ones(8);

 mesh(x)

 pause % strike a key

 y=fft2(x);

 z=real(sqrt(y.^2));

 mesh(z)

 pause

 w=fftshift(z);

 surf(w)

 pause

 contour(log(w+1))

 prism

 pause

 plot(w(1:32,14:16))

 title('fft')

 xlabel('frequency')

 ylabel('modulus')

 grid

 echo off

The echo function displays the operation being currently executed. The program creates a 8-by-8 square on a 32x32 background and performs a 2D FFT on it. The intensity of the FFT (the real part of y) is stored in z and the D.C. term is moved to the centre in w. Note that the plot command when given a 3 by 32 array displays 3 curves of 32 points each.