function [w,y,y_theta] = mtt_sfreq(system_name,theta,free);
## usage: [w,y,y_theta] = mtt_sfreq(system_name,theta,free);
##
## Frequency response with name system_name and parameter vector theta
## The order of components in theta is determined in system_numpar.txt:
## y_theta contains the corresponding sensitivity functions
## Assumes system generated by the sBG approach
## Copyright (C) 1999 by Peter J. Gawthrop
## $Id$
## Assumes SISO system
global mtt_n_parameters mtt_parameters # Global "argc argv"
global mtt_w # Frequencies (if not specified in simpar file
N = length(theta);
eval(sprintf("[nx,ny,nu,nz,nyz] = %s_def;", system_name));
if nargin<3
free = 1;
endif
y_theta = [];
if length(free)==0
free=1; # Make the loop happen once to get y and X
endif
[n,m] = size(free);
if m==1
free = free';
endif
eval(sprintf("%s_simpar;", system_name)); # Read the "simulation"
# parameters
if exist("mttwmin") # Compute frequency range
w = logspace(mttwmin,mttwmax,mttwsteps)'; # Frequency range
else # use global mtt_w
w = mtt_w;
endif
y_theta = [];
mtt_n_parameters = 1+N;
mtt_parameters(2:1+N) = theta; # The actual parameters
for i = free
mtt_parameters(1) = i; # Select wich sens. function
eval(sprintf("%s_numpar;", system_name)); # Read the parameters
eval(sprintf("[A,B,C,D,E] = %s_dm;", system_name)); # Evaluate the
# descriptor matrices
fr = dm2fr(A,B,C,D,E,w);
y_theta = [y_theta fr(:,2)]; # Sensitivity frequency response
endfor
y = fr(:,1); # Actual frequency response
endfunction