Time varying reference

chris · August 11, 2020, 12:54pm

Hi alltogether,

I am new to acados and trying to set up my first running example. I would like to use a linear least squares term and provide a time varying reference y_ref similar to:
http://acado.sourceforge.net/matlab/doc/html/matlab/acado/packages/+acado/@OCP/minimizeLSQ.html

I checked all the matlab examples, but I could not find an example as all of them use a constant y_ref over the horizon. Also all my tries where not successful.

Do you know how to provide a time varying reference?

Thanks a lot!

FreyJo · August 12, 2020, 10:07am

Hi Chris,

welcome to the forum!

You can set the y_ref value stage wise after creating the solver, as it is done here:

github.com

acados/acados/blob/1736ea73acfb71f34a067d77c9f0e565be6cf3a5/examples/acados_matlab_octave/test/test_ocp_pendulum_on_cart.m#L269


% change number of sqp iterations
ocp.set('nlp_solver_max_iter', 20);

% modify numerical data for a certain stage
some_stages = 1:10:N-1;
for i = some_stages
    if (strcmp(cost_type, 'linear_ls'))
        ocp.set('cost_Vx', Vx, i); % cost_y_ref, cost_Vu, cost_Vx, cost_W, cost_Z, cost_Zl,...
         % cost_Zu, cost_z, cost_zl, cost_zu;
        ocp.set('cost_Vu', Vu, i);
        ocp.set('cost_y_ref', yr, i);
    end
    if ng > 0
        ocp.set('constr_C', C, i);
        ocp.set('constr_D', D, i);
        ocp.set('constr_ug', ubu, i);
        ocp.set('constr_lg', lbu, i);
    end
end

% solve

Cheers,
Jonathan

chris · August 14, 2020, 8:17am

Hey Jonathan,

thank you for your quick response! In this example the reference is passed in a loop scalar-wise. Is there a possibility to pass it as a vector in one function call?

Greetings
Christian

FreyJo · August 14, 2020, 9:01am

If you want to set the same y_ref value for multiple subsequent stages, say stage s0 to stage se.
You can do something like this:

    ocp.set('cost_y_ref', yr, s0, se);

Otherwise, you will have to use multiple function calls.

Cheers