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Frequency response estimation requires an
input signal at the linearization input point to excite the model
at frequencies of interest, such as a chirp or sinestream signal.
A *sinestream* input signal is a series of sinusoids,
where each sine wave excites the system for a period of time. You
can inject the input signal anywhere in your model and log the simulated
output, without having to modify your model.

Frequency
response estimation adds the input signal you design to the existing Simulink^{®} signals
at the linearization input point, and simulates the model to obtain
the output at the linearization output point. For more information
about supported input signals and their impact on the estimation algorithm,
see Creating Input Signals for Estimation.

For multiple-input multiple-output (MIMO) systems, frequency
response estimation injects the signal at each input channel separately
to simulate the corresponding output signals. The estimation algorithm
uses the inputs and the simulated outputs to compute the MIMO frequency
response. If you want to inject different input signal at the linearization
input points of a multiple-input system, treat your system as separate
single-input systems. Perform independent frequency response estimations
for each linearization input point using `frestimate`,
and concatenate your frequency response results.

Frequency response estimation correctly handles open-loop linearization input and output points. For example, if the input linearization point is open, the input signal you design adds to the constant operating point value. The operating point is the initial output of the block with a loop opening.

The estimated frequency response is related to the input and output signals as:

where *u _{est}(t)* is
the injected input signal and

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