As mentioned above, cyclic convolution can be written as
where

and

. It is instructive to interpret this
expression
graphically, as depicted in Fig.
7.5 above. The
convolution result at time

is the
inner product of

and

, or

. For the next time instant,

, we shift

one sample to the right and repeat the
inner product operation to obtain

,
and so on. To capture the cyclic nature of the convolution,

and

can be imagined plotted on a
cylinder.
Thus, Fig.
7.5 shows the cylinder after being ``cut'' along the
vertical line between

and

and ``unrolled'' to lay flat.
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