4.6.2 Greatest hits from previous weeks

4.6.2.1 How to add a vertical line to a plot

http://mathematica.stackexchange.com/questions/3561/how-to-add-a-vertical-line-to-a-plot

 
In the plot below I would like to add two vertical lines at $x = \frac{\pi}{15} \pm \frac{1}{20}$. 
How can I do that? 
 
f[x_] := (x^2 z)/((x^2 - y^2)^2 + 4 q^2 x^2) /. {y -> /15, z -> 1, q ->  ...
 

- asked by sjdh (32 votes), answered by Ajasja (48 votes)

4.6.2.2 Calculate the 2D Fourier transform of an Image

http://mathematica.stackexchange.com/questions/29203/calculate-the-2d-fourier-transform-of-an-image

 
I am new to Mathematica, and using version 8.0. 
 
I would like to calculate the 2D Fourier Transform of an Image with Mathematica and plot the magnitude and phase spectrum, as well as reconstruct the  ...
 

- asked by user8727 (5 votes), answered by Nasser (27 votes)