[ninf,fpeak]
= hinfnorm(___) also returns the frequency, fpeak,
at which the peak gain or largest singular value occurs. You can use
this syntax with any of the input arguments in previous syntaxes.
If sys is unstable, then fpeak = Inf.

Relative accuracy of the peak gain, specified as a positive
real scalar value. hinfnorm calculates ninf such
that the fractional difference between ninf and
the true H_{∞} norm
of sys is no greater than tol.

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

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

If sys is a single unstable model,
then fpeak is Inf.

If sys is a model array, then fpeak is
an array of the same size as sys.In this case, fpeak(k) is
the peak gain or largest singular value frequency of the kth
model in the array.