Robust Control Toolbox™

Create options object for use with wcgain, wcsens, and wcmargin

Syntax

• options = wcgopt 
  options = wcgopt('name1',value1,'name2',value2,...) 
  wcgopt
  

Description

options = wcgopt (with no input arguments) creates an options object with all the properties set to their default values.

options = wcgopt('name1',value1,'name2',value2,...) creates a wcgain, wcsens and wcmargin options object called options in which specified properties have specific values. Any unspecified property is set to its default value. It is sufficient to type only enough leading characters to define the property name uniquely. Case is ignored for property names.

wcgopt with no input or output arguments displays a complete list of option properties and their default values.

The following are the wcgopt object properties:

Object Property	Description
Sensitivity	Computes margin sensitivity to individual uncertainties {`off'; `on'}. Default is 'on'
LowerBoundOnly	If LowerBoundOnly is 'on', then only the lower bound computation is performed. The default value is 'off', which implies that both upper and lower bounds for worst-case gain are computed.
FreqPtWise	Apply stopping criteria based on upper/lower bounds (described below) at every frequency point (as opposed to just the peak value). FreqPtWise=1 activates the pointwise criteria. In order to only compute the peak value to within tolerance, use 0. Default = 0.
ArrayDimPtWise	Relevant for uss/ufrd/ss/frd arrays. For indices specified in ArrayDimPtWise, the stopping criteria based on upper/lower bounds (described below) is used at every point in array dimensions specified in ArrayDimPtWise, being applied to the peak value over all other array dimensions. Default = []. If FreqPtWise==1, the computation terminates when at least one of the following four conditions is true at every frequency: UpperBound - LowerBound <= AbsTol UpperBound - LowerBound <= Reltol*UpperBound UpperBound <= AGoodThreshold + MGoodThreshold*Norm(NominalValue) LowerBound >= ABadThreshold + MBadThreshold*Norm(NominalValue) If FreqPtWise==0, the computation terminates when any one of the following four conditions is true: PeakUpperBound - PeakLowerBound <= AbsTol PeakUpperBound - PeakLowerBound <= Reltol*PeakUpperBound at every frequency UpperBound <= AGoodThreshold + MGoodThreshold*Norm(NominalValue)) at some frequency LowerBound >= ABadThreshold + MBadThreshold*Norm(NominalValue) In both situations above, the stopping condition is applied at every point in array dimensions specified in ArrayDimPtWise. UpperBound and LowerBound are the peak values over all other array dimensions.
Default	Structure with default values of all wcgopt properties.
Meaning	Structure. Field names are wcgopt properties, and values are the text description of property.
VaryUncertainty	Percentage variation of uncertainty used as a step size in finite-difference calculations to estimate sensitivity. Default is 25.
AbsTol	Upper and lower absolute stopping tolerance. Default=0.02.
RelTol	Upper and lower absolute stopping tolerance. Default = 0.02.
AbsTol	Upper and lower relative stopping tolerance. Default=0.05.
MGoodThreshold	Multiplicative (UpperBound) stopping threshold. Default = 1.04.
AGoodThreshold	Additive (UpperBound) stopping threshold. Default = 0.05.
MBadThreshold	Multiplicative (LowerBound) stopping threshold, Default = 5.
AGoodThreshold	Additive (LowerBound) stopping threshold. Default = 20.
NTimes	Number of restarts in lower bound search (positive integer).
MaxCnt	Number of cycles in lower bound search (positive integer). Default = 3.
MaxTime	Maximum computation time allowed (in seconds). The computation is prematurely terminated if this much real time elapses before the computation is complete. All quantities that have been computed are returned. Default = 720.

Examples

You can create a wcgopt options object called opt with all default values.

• opt = wcgopt 
  Property Object Values: 
          Sensitivity: 'on' 
       LowerBoundOnly: 'off' 
           FreqPtWise: 0 
       ArrayDimPtWise: [] 
      VaryUncertainty: 25 
              Default: [1x1 struct] 
              Meaning: [1x1 struct] 
               AbsTol: 0.0200 
               RelTol: 0.0500 
       MGoodThreshold: 1.0400 
       AGoodThreshold: 0.0500 
        MBadThreshold: 20 
        ABadThreshold: 5 
               NTimes: 2 
               MaxCnt: 3 
              MaxTime: 720 
  

The following statements change the absolute tolerance stopping criterion from 0.02 to 0.04 and the point wise over frequency test from the peak worst-case value, opt.FreqPtWise=0, to the worst-case value at every frequency.

• opt = wcgopt; 
  opt.AbsTol = 0.04; 
  opt.FreqPtWise = 1; 
  opt 
  Property Object Values: 
          Sensitivity: 'on' 
       LowerBoundOnly: 'off' 
           FreqPtWise: 1 
       ArrayDimPtWise: [] 
              Default: [1x1 struct] 
              Meaning: [1x1 struct] 
      VaryUncertainty: 25 
               AbsTol: 0.0400 
               RelTol: 0.0500 
       MGoodThreshold: 1.0400 
       AGoodThreshold: 0.0500 
        MBadThreshold: 20 
        ABadThreshold: 5 
               NTimes: 2 
               MaxCnt: 3 
              MaxTime: 720 
  

This statement makes a single call to wcgopt to set the maximum computation time to 10000 seconds and disables the Sensitivity calculation.

• opt = wcgopt('MaxTime',10000,'Sensitivity','off'); 
  

See Also
dkitopt     Creates a dksyn options object

robopt      Creates a robustperf/robuststab options object

wcgain      Calculates worst-case gain of a system

wcnorm      Calculates worst-case gain of a matrix

wcsens      Calculates worst-case sensitivities for a feedback loop

wcmargin    Calculates worst-case margins for a feedback loop

Provide feedback about this page

wcgain

wcmargin

© 1984-2008- The MathWorks, Inc.    -   Site Help   -   Patents   -   Trademarks   -   Privacy Policy   -   Preventing Piracy   -   RSS