Example

> a = 0:2*pi:0.5
 a =
 matrix columns 1 thru 6
        0        0.5          1        1.5          2        2.5  

 matrix columns 7 thru 12
        3        3.5          4        4.5          5        5.5  

 matrix columns 13 thru 13
        6 
> sin(a)
 matrix columns 1 thru 6
        0      0.479      0.841      0.997      0.909      0.598  

 matrix columns 7 thru 12
    0.141     -0.351     -0.757     -0.978     -0.959     -0.706  

 matrix columns 13 thru 13
   -0.279  
> fft(sin(a))
 matrix columns 1 thru 3
            -0.0617 + 0i           0.605 - 6.35i         -0.126 + 0.286i

 matrix columns 4 thru 6
         -0.115 + 0.141i        -0.112 + 0.0816i        -0.111 + 0.0439i

 matrix columns 7 thru 9
        -0.111 + 0.0139i        -0.111 - 0.0139i        -0.111 - 0.0439i

 matrix columns 10 thru 12
        -0.112 - 0.0816i         -0.115 - 0.141i         -0.126 - 0.286i

 matrix columns 13 thru 13
           0.605 + 6.35i
> a = rand(4,4)
 a =
        1     0.0369      0.204       0.91  
    0.975      0.162      0.167      0.112  
    0.647      0.665      0.655      0.299  
    0.333     0.0847      0.129      0.265  
> fft(fft(a)')
 matrix columns 1 thru 3
              6.64 + -0i         -0.115 + 0.603i              2.19 + -0i
            1.8 + 0.638i            1.03 + 1.84i         -0.223 + 0.377i
               1.58 + 0i        -0.0817 + 0.757i             -0.384 + 0i
            1.8 - 0.638i          0.573 - 0.636i         -0.223 - 0.377i

 matrix columns 4 thru 4
         -0.115 - 0.603i
          0.573 + 0.636i
        -0.0817 - 0.757i
            1.03 - 1.84i
> abs(fft(fft(a)'))
     6.64      0.614       2.19      0.614  
     1.91       2.11      0.438      0.856  
     1.58      0.761      0.384      0.761  
     1.91      0.856      0.438       2.11