Gilbert Strang, author of the classic textbook *Linear Algebra and Its Applications*, referred to the Fast Fourier Transform, or FFT, as **the most important numerical algorithm in our lifetime**. 

[Wikipedia][1] presents butterfly as "a portion of the computation that combines the results of smaller discrete Fourier transforms (DFTs) into a larger DFT, or vice versa (breaking a larger DFT up into subtransforms). The name "butterfly" comes from the shape of the data-flow diagram in the radix-2 case ..."

The question is: What was the first time that FFT was represented by *Butterfly Diagram* ? References would be appreciated.


  [1]: http://en.wikipedia.org/wiki/Butterfly_diagram