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| R2012a Documentation → System Identification Toolbox | |
Learn more about System Identification Toolbox |
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| Contents | Index |
t=pwlinear('NumberOfUnits',N)
t=pwlinear('BreakPoints',BP)
t=pwlinear(Property1,Value1,...PropertyN,ValueN)
pwlinear is an object that stores the piecewise-linear nonlinear estimator for estimating Hammerstein-Wiener models.
You can use the constructor to create the nonlinearity object, as follows:
t=pwlinear('NumberOfUnits',N) creates a piecewise-linear nonlinearity estimator object with N breakpoints.
t=pwlinear('BreakPoints',BP) creates a piecewise-linear nonlinearity estimator object with breakpoints at values BP.
t=pwlinear(Property1,Value1,...PropertyN,ValueN) creates a piecewise-linear nonlinearity estimator object specified by properties in pwlinear Properties.
Use evaluate(p,x) to compute the value of the function defined by the pwlinear object p at x.
Use pwlinear to define a nonlinear function
, where F is
a piecewise-linear (affine) function of x and
there are n breakpoints (xk,yk), k =
1,...,n. yk =
F(xk). F is
linearly interpolated between the breakpoints. y and x are
scalars.
F is also linear to the left and right of the extreme breakpoints. The slope of these extension is a function of xi and yi breakpoints. The breakpoints are ordered by ascending x-values, which is important when you set a specific breakpoint to a different value.
There are minor deviations from the breakpoint values you set and the values actually stored in the object because the toolbox represent breakpoints differently internally.
You can include property-value pairs in the constructor to specify the object.
After creating the object, you can use get or dot notation to access the object property values. For example:
% List all property values get(p) % Get value of NumberOfUnits property p.NumberOfUnits
| Property Name | Description |
|---|---|
| NumberOfUnits | Integer specifies the number of breakpoints. For example: pwlinear('NumberOfUnits',5) |
| BreakPoints | 2-by-n matrix containing the breakpoint x and y value, specified using the following format: [x1,x2, ...., xn;y1, y2, ..., yn]. If set to a 1-by-n vector, the values are interpreted as x-values and the corresponding y-values are set to zero. |
Use pwlinear to specify the piecewise nonlinearity estimator in Hammerstein-Wiener models. For example:
m=nlhw(Data,Orders,pwlinear('Br',[-1:0.1:1]),[]);The piecewise nonlinearity is initialized at the specified breakpoints. The breakpoint values are adjusted to the estimation data by nlhw.
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