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Fit frequency response data with state-space model
B = fitfrd(A,N) B = fitfrd(A,N,RD) B = fitfrd(A,N,RD,WT)
B = fitfrd(A,N) is a state-space object with state dimension N, where A is an frd object and N is a nonnegative integer. The frequency response of B closely matches the D-scale frequency response data in A.
A must have either 1 row or 1 column, although it need not be 1-by-1. B will be the same size as A. In all cases, N should be a nonnegative scalar.
B = fitfrd(A,N,RD) forces the relative degree of B to be RD. RD must be a nonnegative integer. The default value for RD is 0. If A is a row (or column) then RD can be a vector of the same size as well, specifying the relative degree of each entry of B. If RD is a scalar, then it specifies the relative degree for all entries of B. You can specify the default value for RD by setting RD to an empty matrix.
B = fitfrd(A,N,RD,WT) uses the magnitude of WT to weight the optimization fit criteria. WT can be a double, ss or frd. If WT is a scalar, then it is used to weight all entries of the error criteria (A-B). If WT is a vector, it must be the same size as A, and each individual entry of WT acts as a weighting function on the corresponding entry of (A-B).
Numerical conditioning problems arise if the state order of the fit N is selected to be higher than required by the dynamics of A.