| System Identification Toolbox | |
Select the step-size for numerical differentiation.
Syntax
Description
The function pem uses numerical differentiation with respect to the model parameters when applied to state-space structures. The same is true for many functions that transform model uncertainties to other representations.
The step-size used in these numerical derivatives is determined by the M-file nuderst. The output argument nds is a row vector whose k-th entry gives the increment to be used when differentiating with respect the k-th element of the parameter vector pars.
The default version of nuderst uses a very simple method. The step-size is the maximum of 
times the absolute value of the current parameter and 
. You can adjust this to the actual value of the corresponding parameter by editing nuderst. Note that the nominal value, for example 0, of a parameter may not reflect its normal size.
| | noisecnv | nyquist | |