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The highest frequency
in equation (11),
,is almost .This frequency is twice as high as the Nyquist frequency .The **Nyquist frequency**
is normally thought of as the ``highest possible'' frequency,
because , for integer *t*,
plots as .The double Nyquist frequency function,
, for integer *t*,
plots as .So this frequency above the highest frequency is really zero frequency!
We need to recall that .Thus, all the frequencies near the upper end of the range equation (11)
are really small negative frequencies.
Negative frequencies on the interval were moved to interval by the matrix form of Fourier summation.
A picture of the Fourier transform matrix is shown in Figure 1.
Notice the Nyquist frequency is the center row
and center column of each matrix.

**matrix
**

Figure 1
Two different graphical means of showing the
real and imaginary parts of the Fourier transform
matrix of size .

** Next:** Laying out a mesh
** Up:** FOURIER TRANSFORM
** Previous:** FT as an invertible
Stanford Exploration Project

12/26/2000