res2tf, res2xf

SDT-base Contents Functions

res2tf, res2xf

Purpose

Create the polynomial representation associated to a residue model.
Compute the FRF corresponding to a residue model.

Syntax

[num,den] = res2tf(res,po,idopt)
xf        = res2xf(res,po,w,idopt)
xf        = res2xf(res,po,w,idopt,RetInd)

Description

For a set of residues res and poles po (see res ), res2tf generates the corresponding polynomial transfer function representation (see tf )).

For a set of residues res and poles po, res2xf generates the corresponding FRFs evaluated at the frequency points w. res2xf uses the options idopt.Residual, .DataType, AbscissaUnits, PoleUnits, FittingModel. (see idopt for details).

The FRF generated correspond to the FRF used for identification with id_rc except for the complex residue model with positive imaginary poles only idopt.Fit='Posit' where the contributions of the complex conjugate poles are added.

For MIMO systems, res2tf and res2xf do not restrict the pole multiplicity. These functions and the res2ss, qbode sequence are thus not perfectly equivalent. A unit multiplicity residue model for which the two approaches are equivalent can be obtained using the matrices new_res and new_po generated by id_rm

 [psib,cpsi,new_res,new_po]=id_rm(IIres,IIpo,idopt,[1 1 1 1]);
 IIxh = res2xf(new_res,new_po,IIw,idopt);

The use of id_rm is demonstrated in demo_id.