function [par,Par,Error,Y] = ppp_identify (system_name,u,y_0,par_names,par_0,extras)
## ppp_identify: System identification for PPP
## usage: [par,Par,Error,Y] = ppp_identify(system_name,u,y_0,par_names,par_0,extras)
##
## system_name String containing system name
## u System input (column vector, each row is u')
## y_0 Desired model output
## par_names Column vector of (padded) strings - the adjustable
## parameter names
## par_0 Initial parameter vector estimate
## extras (opt) optimisation parameters
## .criterion convergence criterion
## .max_iterations limit to number of iterations
## .v Initial Levenberg-Marquardt parameter
if nargin<6
extras.criterion = 1e-5;
extras.max_iterations = 10;
extras.v = 1e-5;
extras.verbose = 0;
endif
s_system_name = sprintf("s%s", system_name); # Name of sensitivity system
## Set up parameters
sim = eval([s_system_name, "_simpar;"]); # Simulation parameter
sym = eval([s_system_name, "_sympar;"]); # Parameter names
x0 = eval([s_system_name, "_state(par_0);"]); # Initial state
# ## Set up the free parameter list
# free = [];
# [n,m] = size(par_names);
# for i = 1:n
# p_name = deblank(par_names(i,:));
# s_name = sprintf("%ss", p_name);
# if struct_contains(sym, p_name)
# i_p = eval(sprintf("sym.%s;", p_name));
# if struct_contains(sym, s_name)
# i_s = eval(sprintf("sym.%s;", s_name));
# free_i = eval(sprintf("[%i,%i];", i_p, i_s));
# free = [free; free_i];
# else
# printf("Sensitivity parameter %s does not exist: ignoring \
# parameter %s\n", s_name, p_name);
# endif
# else
# printf("Parameter %s does not exist: ignoring\n", p_name)
# endif
# endfor
# free
free = ppp_indices(par_names,sym);
[par,Par,Error,Y] = ppp_optimise(s_system_name,x0,par_0,sim,u,y_0,free,extras);
endfunction