Wikipedia 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.
Best Answer
A little idle google scholaring on "fft and butterfly" (restricted to the years 1965-1970) turned up a 1969 Lincoln Laboratory Technical Report (#468), "Quantization Effects in Digital Filters," by C.J. Weinstein, which contains the phrase,
beside a figure that does indeed look like a plausible geometric sketch of a butterfly.
The report is available at http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD0706862 . Portions of it, including the "butterfly" figure, reappear in a joint paper with A.V. Oppenheim, "Effects of Finite Register Length in Digital Filtering and the Fast Fourier Transform," published in 1972 in the Proceedings of the IEEE (vol. 60, no. 8, pp. 957-976, available at http://www.rle.mit.edu/dspg/documents/EffectsFFTComplete.pdf .