Problem in using ZeroMQ library from CoppeliaSim in Matlab

Hi All

runnign commands using ZeroMQ in Matlab to pilot CoppeliaSim has turned with this error :

Output argument "varargout{2}" (and possibly others) not assigned a value in the execution with "RemoteAPIObject/subsref"
function.

Error in VrepConnectorZMQ (line 21)
[~,obj.robot_joints(i)] = obj.sim.getObject(strcat('/LBR_iiwa_14_R820_joint',int2str(i)));

Error in main (line 78)
robot = VrepConnectorZMQ();

The class code was :

classdef VrepConnectorZMQ


    properties
        sim;				%Similar to fd
        client;			%Used for server connection and server requests
        robot_joints = []	%List of joint handles
        		%Integration step used for simulation
    end

    methods

        function obj = VrepConnectorZMQ()
            addpath vrep_lib/;						%Adding the APIs to the path
            client = RemoteAPIClient();
            client.setStepping(true);               	
            obj.sim = client.getObject('sim');			%RemoteAPI object
            obj.sim.startSimulation();

            for i = 1:7 
                [~,obj.robot_joints(i)] = obj.sim.getObject(strcat('/LBR_iiwa_14_R820_joint',int2str(i)));
            end
        
            for i = 1:7
                [~, joint_pos] = obj.sim.getJointPosition(obj.robot_joints(i));
            end
            % When simulation is not running, ZMQ message handling could be a bit
            % slow, since the idle loop runs at 8 Hz by default. So let's make
            % sure that the idle loop runs at full speed for this program:
            defaultIdleFps = sim.getInt32Param(sim.intparam_idle_fps);
            sim.setInt32Param(sim.intparam_idle_fps, 0);
        end

and in the main file it was only called :

        robot = VrepConnectorZMQ();

Answer 1

[Himanshu]

Hello Farzad,

I understand that you are facing an error related to the "Output argument not assigned a value" in your MATLAB code when attempting to run commands using ZeroMQ to control CoppeliaSim.

The error occurs because you are not capturing the output of the "obj.sim.getObject" function call.

To fix this issue, you need to properly capture the output of the "obj.sim.getObject" function and ensure that all required output arguments are assigned values. Since you are assigning values to elements of "robot_joints", make sure to initialize it as an array before the loop.

% initialize robot_joints array
obj.robot_joints = zeros(1, 7);
for i = 1:7
    [~, obj.robot_joints(i)] = obj.sim.getObject(strcat('/LBR_iiwa_14_R820_joint', int2str(i)));
end

I hope this helps.