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Compute poles of dynamic system

`pole(sys)`

`pole(sys)` computes the
poles `p` of the SISO or MIMO dynamic system model `sys`.

If `sys` has internal delays, poles are obtained
by first setting all internal delays to zero (creating a zero-order
Padé approximation) so that the system has a finite number of
zeros. For some systems, setting delays to 0 creates singular algebraic
loops, which result in either improper or ill-defined, zero-delay
approximations. For these systems, `pole` returns
an error. This error does not imply a problem with the model `sys` itself.

Multiple poles are numerically sensitive and cannot be
computed to high accuracy. A pole *λ* with
multiplicity *m* typically gives rise to a cluster
of computed poles distributed on a circle with center *λ* and
radius of order

where ε is the relative machine precision (`eps`).

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