Can't process 1-dimension state system

[utotch]

I found nlgreyfast can't process "1D-state" system when I solve my problem.

When I code both "fopts.x0_free_v = false" and "fopts.x0_free_v = true", nlgreyfast can't proceed.
I think it is caused that nlgreyfast expects over 2D state system.

But I have a practical 1D state nonlinear system problem, and I believe 1D state system should not be ignored to solve.

I show the code:

% nlgreyfast sample
% dx/dt = theta*x + u
% estimate theta
x = casadi.MX.sym('x');
u = casadi.MX.sym('u');
theta = casadi.MX.sym('theta');
n_param = 1;
rhs = theta*x + u;
ode = casadi.Function('ode', {x, u, theta}, {rhs});
sample_freq = 20.0;
num_sample_sim = 100;
num_steps_per_sample = 10;
[model, all_samples] = nlsim(ode, sample_freq, num_sample_sim, num_steps_per_sample);
fopts = struct;
fopts.scale_v       = ones(n_param,1);
fopts.param_guess_v = 1.0;
fopts.param_lb_v    = -10;
fopts.param_ub_v    =  10;
fopts.x0_v          = 0.5;
fopts.x0_free_v     = false; % both [true] and [false] causes problem
fopts.y_states_v    = [1];
fopts.X_guess_H     = 'guess_mechatronic';
fopts.N_group_size  = 1;

% dataset(train)
dt = 0.1;
ts = (0:dt:100)';
us = sawtooth(ts);
theta_true = -2.0;
sysc = ss(theta_true, 1, 1, 0);
x0 = 0.5;
[ys, ts_, xs] = lsim(sysc, us, ts, x0);
data_train = iddata(ys, us, dt);
plot(data_train);
model_est = nlgreyfast(data_train, model, fopts);
fprintf(2,'[theta(true)    ]%f\n', theta_true);
fprintf(2,'[theta(estimate)]%f\n', model_est.param_est_v);
fprintf(2,'[x0(true)       ]%f\n',  x0);
fprintf(2,'[x0(estimate)   ]%f\n',  model_est.x0_est_v);

"fopts.x0_free_v = false" case

Error using casadi.MX/paren_asgn
.../casadi/core/mx.cpp:330: Dimension mismatch. lhs is [0,0], while rhs is [0,1]

Error in indexing (line 42)
        paren_asgn(self, v, s.subs{:});

Error in nlidcomb (line 56)
x0_sym_v(x0_free_indexes_v) = x0_decvars_v;

Error in nlgreyfast (line 69)
    [estmodel.param_est_v, estmodel.x0_est_v, estmodel.diag_data ] = nlidcomb(plant_next, fs, u_data_V, y_data_V, ...

Error in nlgreyfast_sample_1d (line 35)
model_est = nlgreyfast(data_train, model, fopts);

"fopts.x0_free_v = true" case

Error using assert
Assertion failed.

Error in nlidcomb (line 269)
assert(all(size(X_guess_H)==size(X_simstart_without_x0_H)));

Error in nlgreyfast (line 69)
    [estmodel.param_est_v, estmodel.x0_est_v, estmodel.diag_data ] = nlidcomb(plant_next, fs, u_data_V, y_data_V, ...

Error in nlgreyfast_sample_1d (line 35)
model_est = nlgreyfast(data_train, model, fopts);