show the same modulus as is shown in Fig. 11.1 for G) to @). These bispectra are repre- 
sented by a bispectrum in the first octant G) where |w3| = @ = w2. The bispectrum is 
shown by the modulus and the phase angle. 
Ea @, + @2+ @; =0 
Fig. 11.1. Symmetric character of bispectrum. 
(From Yamanouchi and Ohtsu.78) 
The points marked O in sub—octants Q), G): ©) (9). and (10) show the same 
bispectra, equal to Syxx(@1, @2) at mark O in octant Q), and the bispectra at points Xx in 
the six sub—octants @). ), @; (8), @), and @2) show its conjugate. Also in Fig. 
11.1, the segments of line in each sub—octant are shown marked by short lines +, +f, +t 
that correspond to the segmented line AB +, BC+, CD + in octant @) that shows the 
same bispectrum. At a fixed frequency wz, in Fig. 11.1, the bispectrum along the segment 
BA (wz = 3) shows interference with the two components at the smaller frequencies 
@ and @, that makes w; + w2 = Wg = @3; the spectrum along the segment 
BC (wz = @) shows interference with one smaller frequency component w and one 
higher frequency component w3(w3 = w2 + w)); and the bispectrum along the segment 
CD (wg = @2) shows interference with the components at two higher frequencies 
W3(W3 = W, + W2) and @;. The hexagonal boundary shape in Fig. 11.1 shows the 
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