freqsepOptions

(Not recommended) Options for slow-fast decomposition

freqsepOptions is not recommended. Specify the SepTol option directly as a name-value argument to freqsep (since R2023b). For more information on updating your code, see Version History.

Syntax

opt = freqsepOptions

opt = freqsepOptions(Name,Value)

Description

opt = freqsepOptions returns the default options for freqsep.

opt = freqsepOptions(Name,Value) returns an options set with the options specified by one or more Name,Value pair arguments.

Examples

Separate Nearby Modes by Adjusting Tolerance

Decompose a model into slow and fast components between poles that are closely spaced.

The following system includes a real pole and a complex pair of poles that are all close to s = -2.

G = zpk(-.5,[-1.9999 -2+1e-4i -2-1e-4i],10);

Try to decompose the model about 2 rad/s, so that the slow component contains the real pole and the fast component contains the complex pair.

[Gs,Gf] = freqsep(G,2);

Warning: One or more fast modes could not be separated from the slow modes. 
To force separation, relax the accuracy constraint by increasing the "SepTol" factor 
(see "freqsepOptions" for details).

These poles are too close together for freqsep to separate. Increase the relative tolerance to allow the separation.

options = freqsepOptions('SepTol',5e10);
[Gs,Gf] = freqsep(G,2,options);

Now freqsep successfully separates the dynamics.

slowpole = pole(Gs)

slowpole = -1.9999

fastpole = pole(Gf)

fastpole = 2×1 complex

  -2.0000 + 0.0001i
  -2.0000 - 0.0001i

Input Arguments

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: 'SepTol',5

SepTol — Accuracy loss factor

10 (default) | nonnegative scalar

Accuracy loss factor for slow-fast decomposition, specified as a nonnegative scalar value. freqresp ensures that the frequency responses of the original system, G, and the sum of the decomposed systems G1+G2, differ by no more than SepTol times the absolute accuracy of the computed value of G(s). Increasing SepTol helps separate modes straddling the slow/fast boundary at the expense of accuracy.

Output Arguments

opt — Options for freqsep

freqsepOptions options set

Options for freqsep, returned as a freqsepOptions options set. Use opt as the last argument to freqsep when computing slow-fast decomposition.

Version History

Introduced in R2014a

R2023b: Not recommended

freqsepOptions is not recommended. Specify the SepTol option directly as a name-value argument to freqsep. This table describes the change in the workflow.

Before R2023b	R2023b
opt = freqsepOptions("SepTol",5e10); [Gs,Gf] = freqsep(G,2,opt);	[Gs,Gf] = freqsep(G,2,SepTol=5e10);