gpeak = getPeakGain(sys) returns
the peak input/output gain in absolute units of the dynamic system
model, sys.

If sys is a SISO model, then
the peak gain is the largest value of the frequency response magnitude.

If sys is a MIMO model, then
the peak gain is the largest value of the frequency response 2-norm
(the largest singular value across frequency) of sys.
This quantity is also called the L_{∞} norm
of sys, and coincides with the H_{∞} norm
for stable systems.

If sys is a model that has tunable
or uncertain parameters, getPeakGain evaluates
the peak gain at the current or nominal value of sys.

If sys is a model array, getPeakGain returns
an array of the same size as sys, where gpeak(k)
= getPeakGain(sys(:,:,k)) .

[gpeak,fpeak]
= getPeakGain(___) also returns the frequency fpeak at
which the gain achieves the peak value gpeak,
and can include any of the input arguments in previous syntaxes.

The second argument specifies a relative accuracy of 0.0001.
The getPeakGain command returns a value that is
within 0.01% of the true peak gain of the transfer function.

Relative accuracy of the peak gain, specified as a positive
real scalar value. getPeakGain calculates gpeak such
that the fractional difference between gpeak and
the true peak gain of sys is no greater than tol.

Frequency interval in which to calculate the peak gain, specified
as a 1-by-2 vector of positive real values. Specify fband as
a row vector of the form [fmin,fmax].

Frequency at which the gain achieves the peak value gpeak,
returned as a nonnegative real scalar value or an array of nonnegative
real values. The frequency is expressed in units of rad/TimeUnit,
relative to the TimeUnit property of sys.

If sys is a single model, then fpeak is
a scalar.

If sys is a model array, then fpeak is
an array of the same size as sys, where fpeak(k) is
the peak gain frequency of the kth model in the
array.

getPeakGain uses the algorithm of [1]. All eigenvalue computations are performed
using structure-preserving algorithms from the SLICOT library. For
more information about the SLICOT library, see http://slicot.org.

[1] Bruisma, N.A. and M. Steinbuch, "A Fast
Algorithm to Compute the H_{∞}-Norm of
a Transfer Function Matrix," System Control Letters,
14 (1990), pp. 287-293.